There could be many reasons they don't prompt you to change: they meant to send an email but your notification preferences disallowed it, they sent an email and you missed it, they wanted to keep it quiet, they forgot to add the message and ux flow to change password, or they're incompetent and didn't know they needed to do that.

The Epic thing I've never seen before but that's definitely incompetence and/or a very weird bug that just slipped past them.