If anything most of what we would call "cult films" had bad reviews on top of bad box office earnings on release.

Personally, I would define a cult film as one that was either a critical or commercial flop on release but which developed dedicated fans over time.

A poorly reviewed film that ends up beloved, is a cult film to me.

I mean, while it's not always a factor, reviews have driven people to see otherwise unpopular films in the past, and continue to do so.

Imagine how many people nowadays watched a movie because they saw it on Red Letter Media? A lot of those movies already have cult followings, but the point is that if a random popular YouTube channel decides to cover a random film that few people have seen or heard of, it could develop a cult following afterward.