Rely on 3rd parties they have good relationship with and compared to Xbox an exclusivity is totally different from "hope for the best".
Let's say PD have a lot more leeway than Evolution Studio could had ever got. Besides being semi-independent from Sony so let's not mix stuff here. And on VGC you'll get some very vocal people against GT if you look around. GTS sold more than GT6 and at it worse still oversell any Forza Motorsport so why would Sony close PD?
I think you misunderstand. 3rd parties dont support Playstation because a good relationship per se. Its also about viability.
Japanese gamers keep buying Playstation consoles because they expect good support. Wii U didnt get great support in Japan because it flopped in general.
However, Switch has sold great so many developers are jumping ship and making something of a prioirty. It didnt happen because a relationship went sour, it just makes sense for them to support Switch.
Now is Sony gonna moneyhat a bunch of Japanese games to fight off Switch? I doubt it but maybe. Is Sony gonna make a bunch of games geared towards Japan? Lol, fuck no! Hence, Sony will mostly hope for the best and I think thats fine.
I never suggested Sony should consider closing Polyphany. In fact, I was confused by the closure of Evolution Sudios given Driveclub sold well and they could get a game out faster than Polyphany.
Are we absolutely certain GTS sold better than any Forza game? I think they only announced player numbers. Individual Forza Horizon games were boasting higher player numbers than GTS, so we can only speculate.
More importantly, Forza had six releases this gen and each did good or great. That would mean Forza likely brought in significantly more revenue. Semi annual releases is also good for a service like Game Pass.