I have wondered this myself. I think it's because it's such a part of the culture of those that are ages 15-30, which is the prime demographic of this site, Twitter, Reddit, Facebook, etc etc. That age group grew older, surrounded by Spongebob in every form; merchandise, the show, the movies, the commercials. It's easily accessible, recognizable, understandable, and it can be edited to whatever somebody sees fit.
Or: I don't fucking know, normies love shitty memes or something?
