As for "why solo?", I imagine it's just a response to wanting to game but not having people to play with, which is a conundrum that's bedeviled a fairly large fraction of gamers since the beginning. That spiked during covid, of course; but I've also heard that, in a broad cultural sense,
Americans, at least, have gradually been becoming more solitary over the last decade or two (less eating out, less dating, less exercising, less theater attendance, etc), so that might be driving it too, at least in the US.