Because all the tracks are in Magical Gran Turismo Land where all the race tracks are right next to each other and your car never needs any prep work and your tires only wear out if you want to drive more then 20 laps at a time.
In Magical Gran Turismo Land all cars are street legal, and all modifications are installed in an instant by mystical mod pixies, who look a little like the Pep Boys but don't tell them that.
In Magical Gran Turismo Land no car dealership is more then 3 seconds drive away, except for some that always remain shimmering illusions on the horizon. At the car dealerships, you can see most any car you can think of, and the rarest and most non-existant vehicles can be yours. All production runs are unlimited, all used cars are flawless and you couldn't wreck any of them if you tried.
Don't go as far as the test track though, or the only criminal in all of Magical Gran Turismo Land will break into your mysterious supergarage and steal some of your cars, and do strange things to the other ones.
You can never be finished with Magical Gran Turismo Land unless you are bilingual, because nobody can find the drag strip, so just relax and enjoy and wish you had that much money and that many cars in real life.