There’s another reason why bad films are particularly beloved by cinephiles: they illustrate (by negation) the importance of filmic techniques — particularly, the parts of cinematic language that are so basic and widespread that they lack terminology and are learned by experience. For instance, otherwise-competent scenes intended to be dramatic become comic because of slightly incorrect timing of cuts, showing the incredible emotional manipulation that cut timing by itself can achieve when used carefully.
Understanding what went wrong is a film nerd’s game, since it requires, rewards, and deepens understanding of the mechanics of the medium and conventions; as a result, the best bad movies are those that could have been great but fail in unusual or interesting ways. Most bad movies fail by being boring — doing conventional things in conventional ways and merely being slightly off the mark in creating the right combination to make it passably entertaining — but Manos: The Hands of Fate fails at being boring on the grounds that its filler scenes are out of place, combines some genuinely creepy cinematography with terrible sound design and incomprehensible lines, and keep flubbed takes in. Most bad movies fail by hewing too closely to the genre conventions and becoming predictable, but The Room fails to hew closely enough to a genre whose conventions the author misunderstood, and the result is an interestingly warped reflection with its own built-in hooks for criticism.