The events I most like are somewhere in between a session and a singaround, where there can be solo spots as well everybody-join-in sets. They are perhaps not quite as common as they used to be but they still happen.

But what absolutely does NOT work is people treating solo melody instruments as if they were solo ballad singers, and sitting on their hands when they could be trying some sort of accompaniment for tunes that absolutely require it. It doesn't feel like respect for the music, it feels like being shunned.