I'm the DRI for most of these problems. Random thoughts:
I think David Ogilvy said something like "Search all the parks in your city, you'll find no statues of committees". Everyone was super keen to make OSM in to a web of committees, and this is one root of the problem from an organizational point of view. It's not super clear to me what the OSMF has done in the last (to pick a number) 5 years. (I don't regard "doing the same thing as last year" as relevant to anything, I just have a personal bias towards new things).
From a technical point of view we merged sysadmin (who inherently want stability) with development (who inherently want change) and stability won (it doesn't involve arguments or as much work, I guess). That's why the API looks the same way I designed it X number of years ago.
It's still a wonderful project, but more of a work of art than anything else. It's not like wikipedia didn't have all the same problems. Making a project that really evolves and grows over large periods of time is really hard. Like - most of the things on the S&P 500 won't be there in 10 or 20 years or something.
I think what really happens is that projects go through a lifecycle and something new comes along to replace them, rather than anything getting fixed. I'm not sure if this is a good example, but, you could try to "fix" Apache, or you could just do this new thing, "nginx". For all kinds of reasons, the new thing is more efficient. One of the few counter examples I think is going to be Amazon.
The world has moved on from making vector maps and OSM solved almost all the related problems (just not geocoding, which annoys me no end). It moved on, because of OSM! All the money and interest in maps is now around autonomous navigation, which means 3D maps and other things outside of OSMs area.