removing cars via a patch is one dumb suggestion, more so when you consider it lazy not to do that. So you just want to be able to buy the game and browse the menus?
Most likely it's not every car in the game that is creating the problem. They likely had a 5 year licensing deal with a single car make that is causing the issue, maybe more but probably not every car make in the game. They could go in and patch out all cars by whichever car makes that are creating the issue, but they are instead choosing to kill the game. Kind of sad imo, Driveclub is pretty fun, better than GT anyway though I still prefer Forza Horizon to Driveclub.
As I said before, Forza has the same problem, both Horizon 1 and Horizon 2 have already been delisted due to either expiring car licensing deals, or expiring music licensing deals, and it is possible that Forza Horizon 3 and 4 will also be delisted 4 years after they released like FH1 and FH2 were.
its highly unlikely that a single car had a 5 year license and the rest didn't. a single manufacturer is possible but also unlikely since such long term licensing makes little sense for the car manufacturer with the variety of different car games using their brand there are.
That said, patching is not nearly as easy as you make it out to be. Getting rid of the cars are one thing, but that can easily cause other issues. Additionally, DC has different car iconography all over the menus and even the opening video itself. If an affected car(s) are part of this specific iconography, then they would need to go through the process of changing those too. Manufacturers even have their own stats collected for the player to see, so there is that.
The most difficult part would be the individual races within different leagues, or even whole entire leagues, that would be affected because of a car license. Now these races would need to be patched out (affecting the individual league or just the overall progression system from a visual and structural capacity - which again can cause problems) or they need to be changed with other cars.
Obvious nothing else will be re-licensed so going through changing will be a meaningless move since they will just need to do it again. removing stuff isnt that simple menu UI, stats, and races themselves are going to be majorly affected.
Saying they are being lazy for not just patching out the content seems rather ill-considered. It is not nearly as easy as just removing the cars.
That doesn't excuse Sony for dropping the online servers. But this is risk a company takes when a game they make is based mostly around licensing. And this doesn't even consider the music licensing the game has too.