In cities with good public transport few people take the car to the city center, yet the shops are dead. There also hasn’t been a major reduction in parking over the last couple of decades that would explain the phenomenon.
What do you mean no major reduction? You used to be able to park for free to pop into a shop to quickly grab something, now you have to pay high rates via another different app that you need to install and register your card on before you can even pay and you are fined automatically via CCTV if you run out of time or don't register and pay quickly enough. That did not happen a few decades ago.
Or just go to a supermarket or shopping center where parking is free and easy and you are not being preyed on by parking companies trying dark patterns to fine you.
That's the crux of it. Most places outside of London don't have good public transport.
I can catch a bus but I have to walk to it, it comes at most twice an hour (usually hourly) and it a very circuitous route so it take ages.
Or I can drive 15 minutes from my door but it's expensive to park. So I generally head in the other direction to an out of soulless town shopping centre.
It would be luxury to have something like the Tube arriving every 2 minutes. I love it when I'm in London.