I think the issue is that, until Dark Souls III, the physics in Souls games were tied to the framerate, and so putting someone running at 60fps against another player at 30fps might pose problems.
Then again, I don't remember Dark Souls on PC showing too many problems in that respect, so maybe it wouldn't actually be much of a barrier for Bloodborne.
This would be the actual problem. It definitely did cause weird, game breaking bugs to occur when running at 60fps, so it isn't something most people advised. That said, do we actually know if the framerate is tied to physics in Bloodborne? Perhaps they said something to that effect (And it would makes sense given that other games in the series did it), but without a PC version, I'm not sure we really know that.
If it is the case though, that would absolutely be a good reason not to patch it to a higher FPS.
You can say the same about the other games they're patching.
Sure. The patching is either due to 1.) Wanting a technical showpiece for the improvement, 2.) Wanting to sell upcoming DLC or versions of the game, or 3.) Wanting to build up the brand for future iterations of the series.
I'm not sure if Bloodborne could fall under any of those categories (Thought I'd love it to fall under the third), so the benefit to From and Sony seems minimal at best.