I don't think that people find it outdated as much as limiting. There are just some things that GM and SC can't handle, like for/while loops, threading, extensive networking, etc...
I'm working on a true MMPORPG, and I can tell you that it'd be impossible to make in GameMaker. You can make something multiplayer, but not massively so unless you have socket handling, loops, and more.
Perhaps I'll post the base client soon. You can't do anything except walk around so far, but once I get the base down, it's easy to add on features.
- Ghost