I think a large part of it is that they outsource the ports. Plus in most cases the recent PC re-releases have been ports of the Android/iOS versions that in turn have been ports of DS/PS3 emulated PSone versions. IX PC, for example, is basically running on an Android emulator. I think in most cases it's probably technically more accurate to call some of the re-releases "emulators" rather than actual ports.

Though, of course, that doesn't excuse XIII. XIII-2 I didn't have that many issues with and LR was fine for me.

On that note, aside from being 30 FPS locked, X|X-2 HD has been a pretty solid port for me. I haven't noticed any issues with it.