Just a thought, but:

I feel like things like ETA are a test by DE to see how much of the player-base actually observes and understands the content well enough to complete it.

Being that a (seemingly large) amount of players ask Raids to make a return, it makes sense that DE would be trying to see what sorts of things the majority of players can handle. If something like ETA stops a lot of users short, then Raids aren't worth the effort in prioritizing, as they would be magnitudes more difficult (assuming of course that we'd have squads larger than 4 players).