Yeah, the simplicity is a godsend. Lets you pump out a minimally viable client/bot in minutes with whatever language you like, without having to mess around with an existing framework or library.
I'll second that. For example, here's a bot that logs every channel you invite it to...in 50 lines of shell. How big would the equivalent XMPP bot be (libraries included)?
50 lines of clean comprehensible shell code even! Written with the traditional code-golfed style of shell scripting I bet you could half that without even trying. ;)
https://github.com/acg/logbot/blob/master/bin/logbot.sh