color management is actually super hard to do, so making sure it's done right is very important, so this is one of the few times it actually makes sense. I mean, just take a look at windows, it still looks like shit over there.
Guessing from how this change required 3+ implementations before it became official according to the gitlab page, maybe it's a chicken and egg situation. Hdr is a lot of work so maybe people don't want to implement an unfinalized version that might change
The compositors are the ones doing a lot of the protocol development. They want to have WIP versions so they can see what issues crop up, they've been making versions all doing. Now, I agree that it is slowing things down, but it's more of just an additional thing that needs to get done, not so much a chicken and egg problem.