I like the idea of splitting into different categories, I've seen some people who don't wanna play with the planes or boats so street racing can only allow you to use cars and bikes.
That's true. It's good for the street racing category, but they've also locked professional racing behind the boat racing. Driving F1 cars around a circle may not be the most exciting thing, but I'd want those cars in freeroam ASAP dammit.
Also, on the activities page on the start menu, you can see there are supposed to be more races in the game similar to the one the beta opens up with. If those races are required to unlock more content in the game, then you'll be forced to grind parts for the types of vehicles you don't like until they're good enough to win.