Yes, now I'm reading about it a bit, and repetition (usually being a critical part of what makes something a piece of music to begin with) seems often cited as an important piece of it.

[there's this interesting book] (https://books.google.com/books?hl=en&lr=&id=4a6cAQAAQBAJ&oi=fnd&pg=PP1&dq=info:qZDte-d77AMJ:scholar.google.com&ots=w6GMO6z3_V&sig=N3I6G9Z3lKo-7nDoteWXTRE0Jww#v=onepage&q&f=false) (by a psychologist who studies music perception) that seems to make this hypothesis very clearly, that music is essentially about repetition, and the occurrence of earworms is specifically related to this quality. (i just read the first few pages and skimmed through it, looks interesting though)