If "Classic" cars are so desirable/good looking, why don't they make more just like them?
For two a couple of reasons:
Styling of Cars
Because it simply isn't possible anymore, there is a lot of red tape. As well crash tests modern cars have to pass. For example in order to pass the frontal crash test of today, the front of a car must have a crumple zone - metal in the car that is designed to be crushed in a crash to absorb energy so that the force of a crash does not deform the passenger compartment and crush the occupants. This therefore limits the way cars can be styled as well as it adds a lot of weight to cars. I'll talk about weight later. As well as this, there is side crash test small overlap crash test, and crash tests for pedestrian safety. All with their own indirect sets of restrictions on styling because of the way the metal must be shaped to accommodate the shape of the crumple zones and stronger side pillars etc. You can read more about the American tests here.
There are also 1 million different little regulations different governments set on cars sold in their country. For example cars cannot car from factory as low anymore, the headlight must be a minimum height for road safety. As well as the rear hazard lights must be able to still flash if the trunk/hatch/boot of the car is open. This is so that if the car is stopped on the side of the road and the trunk is open to access a spare tire or something, drivers can still see the lights flashing.
There are many different laws in many different countries covering different subject like this one, each imposing little restrictions on styling that add up.
With regards of older sports car, other than the aforementioned styling, the reason why they are so much more sought after is because they have certain qualities that modern cars lack because of changes in technology and what the modern car buyer wants.
The modern car buyer want comfort, technology, safety, ease of use, and the government wants higher emission & safety standards in every car. While sports cars of old have little to none of those qualities. Weight is a big factor here. Sport cars (generally) used to be a lot lighter because of the lack of these features. No comfort features, at the maximum you'd get air con, and a radio. Or safety, lack of airbags and crumple zones etc. That's it. Everything thing else adds weight. As well as the lack of computers, and electronic systems. Lower weight means the car handles better (can get around a corner quicker), can accelerate faster, and brake faster as well with the same power and the same brakes, because there less weight to move or slowdown.
Lower weight also helps with another factor: fun Cars that weight less feel much more fun than heavy cars because of certain handling characteristics, they turn in fast, and feel more responsive to your inputs, a lighter objects changes direction easier, people who drive "enthusiastically", notice these characteristics. A car that's fun to drive feels like it's immediately responding to you and is communicating to you though the steering and pedals which is explained bellow.
Another benefit of the lack of technology in older cars is the way the steering feels. Not all cars have this, especially brand new cars, but most cars older than 3-4 have something referred to in the auto industry called steering feel. When you turn the wheel of your car, you can feel little vibrations coming through the wheel and can tell what the front wheels are doing, and you can feel the road beneath you when driving "enthusiastically" or turning normally depending on the car. If you've driven a car with it you know what I mean, most people know what I'm talking about.
Feeling these sensations as well as the feeling of the car going over the road in a sports car with a harder ride, makes the driver feel as if s/he is connected with the car and not just there driving it from point A to B it can be quite a lot of fun.
Steering feel usually increases with speed, so the faster you go the more you feel, but with a car with good steering feel you feel more sensations at slower speeds. Older sports cars especially, this was a key focus, back in the day, to have a lot of steering feel. There was no traction & stability control, the feel of the steering wheel would tell you what the front wheels were doing as the feeling of the entire car in general would tell you the limits of the car (what's the fastest speed I can go around this corner without spinning out?)
Modern cars lack this almost totally. Modern steering systems (electric power steering) kill feel totally almost across the board, older cars have either hydraulic power steering (some cars have hydraulic power steering but with little feel), or no power steering at all which would make steering very heavy, but make the sensations coming through the wheel fantastic. It's difficult to describe, but the difference is massive, the steering feels crisp and clear you can feel the road though the wheel. (Toyota has used electric power steering in there cars exclusively for a while now, all there cars had power steering in the 90's which is why a lot of there cars are seen as very boring in the enthusiasts eyes.)
Modern cars lack most sensations because they're not necessary anymore, with stability control and traction control, unless you have no idea what you're doing you won't crash, and its almost impossible to spin out unless you're driving on ice. While you can drive fast, however it doesn't as feel fun because the feeling is too refined, it feels like you're just sitting here telling the car what to do. To get more feeling from a modern sports car, one must drive faster. Which is illegal and dangerous in different ways compared to a old car with no traction/stability control.
In fact these systems are better for an asshat who has no idea what they're doing because its much harder for them to crash, but in the process of this, it kills fun for the person who has the common sense to learn the limits of there car while driving fast.
The everyday car/driver
However for the average modern car buyer, like the one mom or dad drives to soccer practice and takes to work, modern cars are infinetly better, there much safer, and are much less harmful to the environment and people around us. They are loaded with tech and comfort features But for the enthusiastic driver, there's nothing like an older car. Think about this for a second, all points that make classic sports cars so desirable, decrease comfort, or safety, or they aren't necessary anymore because of computer systems. There aren't as many people who want to buy sports cars like that anymore, so the people who do, buy old ones.
Other reasons for desirability
- Older cars are simpler to work on
- Older cars are generally cool
- Lots of old cars have something in explainable, something that cannot be proven on paper, the have character, they have a soul
TL,DR: "Classic" cars are much more fun to drive because they weigh much less due to safety, it isn't possible to style modern cars like classic ones due to safety.