I would mostly ascribe that to Wikipedia being so large that the staff cannot actually successfully ruin it as that would require an impossible level of effort from them.
Probably, once something gets big enough inertia will keep it running for a while, and while the article on any topic of political interest is going to be a mess, more normal topics should typically be saner.
You forgot #5: Wonder why we can't get new editors to join.
I think that would be 4, with the previous 4 becoming 5.