Well, GML is for games, using GML for applications is wrong in every way it is possible. Also, since GML is made for games, it will make the system requirements much higher than otherwise, and make it boot up MUCH slower.
GML, while designed for games, is also now acknowledged in the community as a tool that can produce applications. Although its not ideal, but AfterBlock is made for a game, and its designed in a very game-like way. It doesn't look like your average Windows GUI.
Remember, copy-paste is the root of all evil.
I couldn't copy and paste the content in the project if I tried... it would take weeks.
In response to your programming language suggestion, it is not possible to just learn and become an expert at a programming language overnight. I'd rather use something I am familiar with at the cost of having to work around memory problems than re-learn an entirely new language, when I'm already bogged down. Its not practical.