I think that they were created because the vision of what they wanted wasn’t possible within the constraints of existing solutions. Like there is no world where setuptools ends up shaped like flit, because the underlying goals and desires of those two projects are different.
I think that solving whatever problems people have to contributing to pip is a more tractable problem then getting agreement on something that isn’t pip. These discussions tend to go nowhere, because they devolve into politics about which tool gets blessed as the default.
Pip is already the “default”, so this side steps that. In fact, pip can start adding those features today, without anyone’s permission, and I suspect if they did so the “please provide a unified tool” talking point would just go away, because pip is already the default tool, it’s just implementing the features that people keep asking for.
Further, I don’t really think it’s "fundamentally changing what it does/is any more than adding the wheel sub command changed what it does/is. It’s not like it’s suddenly changing into a blog authoring tool or something.