Yeah Five Nights at Freddy's played a big part of it especially the one I did of Toy Chica.
(we all know why that one was successful lol)
Lots of new artists, artists that are new to digital, artists that want to learn new tricks and those who just like watching people draw love speed paint videos, especially if it's for something that's already popular like Five Nights At Freddy's, Pokémon, RWBY, Attack On Titan etc. Adding a lot of tags before you upload a video or drawing also helps as well. As for DeviantArt I also put my drawings in TONS of groups although I try to be more careful with the characters from my series because I'm trying to avoid getting plagiarized as much as possible until I can get my series copyrighted. Ghah I worry about that more often than I should.