Somewhere between 2000 to 2010 was a golden age when bicycle components were much more cross compatible than before or after. SRAM was almost all Shimano compatible (cog spacing, freehub splines, etc, IIRC the only difference was cable pull for shifting) and for 10 to 11 speed you could drop a Campagnolo wheel into Shimano/SRAM system or vice versa without any noticeable mismatch. And during that time there was basically one common bottom bracket shell standard.
DUB is a crank spindle standard, and fits in lots of different bottom bracket shells. GXP is also a spindle standard that fits in different shells, most typically English threaded.
But to your main point, that there's a handful of modern standards, yep. There seems to be a good reason for each to exist, at least.
Which makes it worse. Not only does a consumer need to figure out the specs for the BB shell on the frame, but also the specs for the crank spindle.
On the plus side, at least Shimano has, so far, mostly stuck with a single spindle. Where SRAM has produced GXP, BB30, and Dub at overlapping points in time and within the same group of components.
And whoever invented BB30 (Cannondale?) needs a kick in the shin. I’ve never been happy with a BB30 frame - they’re all destined to squeak and creak and pop at some point. Maybe a good standard for a race bike that gets torn down frequently, but just terrible for a consumer bike.
I think it's a part of the problem that consumers keep buying race bikes even if they're really not good for all around riding without support from a team mechanic. It wouldn't be difficult to make a reliable and affordable road bike with 95% of the performance of a race bike (disclaimer: I just made up the number) but selling it would be a challenge.
