Please hear me out. Fests are started by the organizers to encourage more of certain types of fics to be added to AO3, right?
Dead Dove fics allow creators to express themselves in certain ways outside of normal fanfiction, which can be a positive thing. However, I've noticed that DD collections in fic fests tend to attract certain types of authors that are adding things to our fandom that we might not necessarily want to encourage. Remember how mad some people were at you that you didn't allow underage in dead dove? Yes, it's those kinds of people foaming at the mouth to contribute to dead dove in a lot of fests. There's been a problem with violent child r--- showing up more often in bts fic tags. And if an individual author likes dead dove and posts it, well fine. But should fanfic fics festivals really encourage dead dove (yes, I know your fest doesn't allow that current topic, but that doesn't change who you're attracting to write it/ who will see how close they can get to writing that topic while loosely staying in the guidelines?) 
As someone who writes in many different fests, my opinion is that fests need to cut down on dead dove categories. Most of us don't want that category at all. If you want to write violent r--- you can write it on your own and not as part of a fest. Fests with this category also draw p--dos to our fandom. I know you've seen those child r fics in the bts tag, you know what I'm talking about. 
You're trying to get more dd prompts, and I think you know why you don't have more . . . Why aren't more of the people excited to write alpha Jimin also excited to contribute to the dd collection? The truth is if you would have allowed underage fics, you'd have had more dead dove prompts by now. Ask yourself why that is, and then think if fests really, really, really need the dead dove category? Is it necessary for big fests, or can you just post those fics on your own time without promoting them on a mass scale? Do big fests need these little niche categories especially if p*dos love them, too? 
What is it you want the writers to contribute to the fandom? I'm not trying to be unkind about this at all, I just honestly want to know if dd is really that valuable for you to include in your fests? Especially when it ends up as a small fraction of what most of the people contributing to your fest want to write. Do you really need to write whatever noncon/incest/whatever fic you're excited to write as part of the fest or can you just post that out of the fest on its own? 
People who like dead dove will get mad at me, but look at fests who don't limit underage stuff, and look at what kind of stuff ends up getting added on AO3 completely sanctioned under fest organizers. Are we supposed to be happy about that? Everyone who only writes main collection stuff needs to up our game, before the BTS tag on AO3 is taken over by p*o and violent re. Fest organizers can make whatever categories they want, but I hope if enough writers refuse to contribute to these categories, that organizers will get the hint of what most of us don't want. 
*TLDR: Dead dove categories are encouraging p*s to add to the BTS tag on AO3. Most people who contribute to fests are completely uninterested in dd. Why include it in fic fests if it's a niche category that causes many problems? **