The relatively new policy on WP to label plugins as “obsolete” is sort of a pain, especially for stable plugins.
While decimal WP releases are about twice a year, each one “requires” all plugins to post an update that specifies compatibility. Unfortunately, it is acutally fairly non-trivial to update a plugins (vs. a theme, which is totally trivial).
So it is a pain to have to do this for 4 or 5 plugins twice a year, and I’m not always very good at doing that. If some incompatibility arises, then for certain they get updated. But WP has in fact tried very hard to maintain its own backward compatibility, so in fact there are many many perfectly fine plugins that are reported to be incompatible. I would guess that only a very tiny fraction are really incompatible.