Definitely agree with this, it's just a pointless mechanic and there's no way to get brand invitations other than by being lucky at roulette tickets (mostly in four-star roulette tickets).
If they were to implement the ability to sell cars, they'll still make it where you can only sell duplicates, as they will not let you get away with having only one example of a certain individual car.
They should also update certain features that will make the game less reliant on roulette tickets, such as making certain upgrades like the following:
- Carbon Propellor Shaft
- Bore-up S
- Stroke-up S
- High Lift Camshaft S
- Titanium Connecting Rods & Pistons
- Ultra-High RPM Turbocharger
- Weight Reduction Stage 5
available in the Tuning Shop.