>>115859sageru is a network with some unrelated groups on it. #qa predates kissu by a couple years and was made without any relation to any of the preexisting channels, like #jp which was made for 4/jp/ shitposters like 15 years ago. It's not a kissu irc server, it's an irc server with #qa on it, like rizon.
But anyway, IRC isn't for most people and it has some people that don't use kissu there. IRC has limitations that don't put it in direct competition with an imageboard so it's a nice side thing, but sageru's anonymity is a strength for some and weakness for most.