Different chain guide mounts... Why? I think there's two types of chain guide mounts, one of them is screwing in screws and another one is using the bottom bracket to hold it in place. Why not just use one type of mount? Is there a reason why they do this? Cuz I'm using the bb one and I don't see any problems. I want to add a chain guide that has a wheel at the bottom of the chainring to hold the chain but all of them are just exclusive for screw in ones.

And also, what's the name for both of them?
Not all frames have threaded bottom brackets with external cups that can be used to mount a chainguide. Frames with press-fit bottom bracket bearings need to provide threaded holes for bolting on a guide.