My main reasons for not touching any collab post here with a barge pole, as someone who's done collabs before;
-They're all so long! 40 chapters? Are you serious!? That's years of my life! I do little 4-24 pages of collabs, not 400 pages.
-They rarely have an example of previous work, writing, collabs, an online presence even, hell, most of the ideas don't have a script. I'm not willing to spend a long time on something that doesn't even have an ending yet.
-Yes, the writing ideas are often a turnoff too. I've not seen many ideas that really struck me, and it doesn't help that the writer often won't want to 'share spoilers' or is wary of someone 'stealing' their amazing idea, so the pitches are bare bones as hell. Or, stolen from whatever comic/manga/anime is hot right now. No thanks.
-And yeah, unpaid is a huge turnoff. My commission rates are $25/hour. If this project isn't going to match that, AND it's not something I care about? Nah.
It just strikes me as people who've read a few comics/webtoons, decided that they can make it big too, and stride into the tapas forums with their big idea expecting to find a drawing slave. Not everyone, but a lot of times. Art is a hard skill, and anyone who's good knows their worth. Imo that's why a lot of them go unanswered, a combination of all of it, but it feels dismissive of how hard art is and how long it takes to master to get to a level of competency.