I privately refer to that as gratuitous crossoveritis. It's when the author throws things into the fic that serve no real purpose and distract from the
story, just because they're cool. Having cameos is fine. Having plot occuring is fine. Throwing in random ingredients without thinking it through has been
the ruin of many a good fic.
One of my favorite examples of too many crossovers spoil the broth is the sadly deceased "Quantum Destinies". A well written story with a unique
premise and some interesting world building, spoilt by the author's desire to throw in absolutely every major anime of the time.
story, just because they're cool. Having cameos is fine. Having plot occuring is fine. Throwing in random ingredients without thinking it through has been
the ruin of many a good fic.
One of my favorite examples of too many crossovers spoil the broth is the sadly deceased "Quantum Destinies". A well written story with a unique
premise and some interesting world building, spoilt by the author's desire to throw in absolutely every major anime of the time.