Won't car companies release old-style vehicles?

Old-fashioned vehicles but with modern internals? Like the Chevrolet in Pulp Fiction or 1966 Ford Thunderbird and such. They're so beautiful

There's a lot more to it than that. Those old designs wouldn't pass modern safety standards, and those designs flat out aren't fuel efficient. Ford tried to bring back the classic T-bird style, and it was a monumental failure. There's no money in it.

It's not a case of refusing to release these models. It's economics and market forces.
Tooling up for new vehicles cost literally millions. Selling such a vehicle has limited market, hence economic madness for any mas producer.
There's a small market for retro vehicles with modern essentials.
One company providing such a service is based in UK selling cars looking like iconic E type jaguars. From outside looks identical. Seats, dashboard etc almost identical. Running gear such as brakes etc very modern so handles much better.
Not cheap.
So there's a limited market but getting a small scale manufacturer to produce is difficult as folk like returns on investments.
You would need to show size of market. Provide data to prove it. Costing needs to be carried out. Profit margin needs to be adequate to sustain any business plan.
Copyright agreements reached etc.

Because swapping out "the internals" isn't as easy as you make it sound. Sure, you could give it a modern dashboard, no problem.

But fitting a completely different engine, shocks, brakes, etc into a frame not designed for them is not anywhere near so simple. In addition, the chassis itself in many cases will not meet modern NTSA regulations - Classic cars get grandfathered in, but a new car (which this would be), would not.

I do agree though, old cars have much more personality than the samey-whichbrandisthatone look of modern cars.