> Russia tried to join NATO itself after that but was rebuffed.
Yes but it's not that simple. First, do you trust Russia in NATO? Given the nefarious things Russia has done over the last 30 years, you can't trust this on the face of it. It would be a very Russian thing to do. By accounts that I've read (open to other readings here) Russia wanted to join in a privileged position as well, versus as "just another country" and wanted to be fast-tracked and so forth.
> The Baltics joined NATO when Russia was still in disarray and aren't as important strategically.
I don't find any sympathy with the disarray argument. That just says "these countries joined NATO when Russia couldn't do anything about it". Your point about strategic importance, though, is well taken. Ukraine is strategically important for many reasons. Some/one of which is that it can undermine Russia's stranglehold on European gas imports.
> This was primarily for domestic consumption and the West picked it up in February/March together with the notion that Putin had gone mad. Hardly anyone talks about either of these theories any longer.
Agreed. I think the simple case is simply that Putin believe(s)(d) that he had enough negotiating power against NATO countries to be able to stop them from inflicting serious damage on Russia after invading Ukraine, and also that because Ukraine (in Putin's words) isn't a state, the fiction would simply collapse once Russia arrived. We don't do a great job and assume that our incentives are the same as someone else's. In this case Putin couldn't give a crap less about dead people and economic destruction. He cares about The Historical Unity of Russians and Ukraine. Perhaps at a much higher cost than we are willing to endure.