> What matters is whether the prospective income from those platforms outweigh the additional dev costs.
Different APIs increase costs. If dev costs were lower for porting games, the platform would see more games.
2) The majority of costs is ongoing support, not writing to a different API.
> 1) Porting costs are not per game but per engine, which can be shared between multiple games.
That's not true. Majority of the costs maybe, but every platform needs its own tweaks, if for nothing else input often very different in a way engine abstractions are usualy not good enough. And then there is DRM, and anti cheats etc, that are quite platform dependent.
In pretty much any engine there are games that work beautifully and games using same engine that are like trash on fire[1]. There is a reason nvidia and amd often have to release new driver with fixes/optimizations for new games.
[1]: I meant cross platform support (where they work decently on one platform but are trash on others), not that game as a whole itself being trash and or buggy.
True but they're still big enough that that cost is significant. Even when diluted across game budgets.
> 2) The majority of costs is ongoing support, not writing to a different API.
Ongoing support is still required for writing to a different API. Ongoing support involves (a) updating in line with API version changes and (b) updating API-integration abstractions in line with game engine API updates. Supporting multiple APIs adds at least some amount of friction to every code-change.
There's also the increase in cost of testing every engine code change across multiple graphics APIs.