The biggest selling points are probably the developer community, the ease of console support, and the larger track record of commercially successful games. Plus if you are a beginner the resources that come with a commercial tool can make a huge difference.
In a perfect world I'd just recommend the open source thing to everyone, but if I knew an artist who wanted to make a game I'm not sure that would be good advice.
Gamemaker is still focused on 2D. I also think its easier for people without programming experience and the design guides you more but is less flexible.
From now on, GameMaker will be free for non-commercial purposes on all non-console platforms.
At the same time, to meet the needs of hobbyist and indie developers, we are introducing a new one-time fee - a commercial licence that is replacing the current Creator/Indie subscriptions.
Nothing changes for developers targeting the consoles, our Enterprise subscription remains the same.
A one time fee for commercial licenses is just as big as the headline, but if console is only available under an enterprise sub then both of the new offers are nerfed by design :/