I feel like crack is a young person's game (the fic kind, obviously). Every fan fiction author I know began writing deliberate badfic or crackfic (save for the like, two, who I know that conform to the stereotype and began writing mary sue romance). The first phase in loving a thing is poking fond fun at it, and when immature, humor is a blunt instrument. Most writers I know either stop writing deliberately 'cracky' things or they do it in subtle, well crafted ways and thus it is no longer crack and merely 'humorous' or 'light-hearted'. I feel inversely to you that crack is usually an audience label - people who label their stories as crack usually do so preemptively or defensively, but for the most part the distinction between crack and/or badfic and mature humor is usually made by the skill of the author and the interpretation of the reader.

I mean, I've written zombie invasions where the heroes were too busy making Shaun of the Dead references to fight properly, but I did it with a straight face and with decent prose, so it's humor (though I might, to protect myself, refer to it as 'a bit cracky' when linking it). If someone took the same premise and didn't pull it off as well, it would likely be labeled as crack no matter what. This is where I also come around to the conclusion that I feel like 'crack' is slapped on things more often to excuse bad quality or poorly executed humor rather than purely bizarre humor.

I did a little writing this week as a treat for myself because otherwise life decided to, in mental health terms, beat me up and take my lunch money. I treated myself to a niche kink. Given work, life, the universe and everything, I despair wondering if I will ever return to the narrative proper, or even more plotty fluff, again.