This is a good question! But maybe a little long to explain.
I use QB64 because my first language was QBasic which I taught myself at school. If you check my profile, you will find a blog link where I describe learning it.
http://blog.hardcoregaming101.net/2010/03/games-ive-made.html
I tried to learn other languages, including Dark Basic, but none were as easy as QBasic. And QB64 is basically QBasic but for modern systems.
I tried Game Maker, as a drag and drop system, but I couldn't even get a text box to show up. It was laborious, cumbersome, slow, and not intuitive.
QBasic and QB64 are very easy to get quick results. If you want to test an idea very quickly, you can just write a few lines and immediately see the result.
After about half an hour of trying to use Game Maker nothing was happening, and I got fed up.
I am not a professional game maker. I do this for fun. So I need to see immediate results to keep myself entertained.
I normally program in QBasic using DOSbox, then compile it using QB64, since QBasic for DOS is actually faster to see results than QB64.
Hope this is useless.
Basically: it's fast and easy, and I'm lazy and just doing this for fun.