While I don't say with 100% certainty...

There's still a lot of people who have not yet done coil, perhaps let alone set foot in it. The major reason for this is because people want static parties, and people want specific party compositions, hence there'll be a lot of, say...melee DPS players who probably still don't have a team they are raiding with.

At least Crystal Tower will give them an opportunity to gear up to iLevel 80 while they look for a team. Also, good for gearing alts. And finally, Coil can only be completed once a week, which means iLevel 90 gear isn't very farmable to begin with. At the very least, you can still replace your current DL parts with iLevel 80 parts as you prepare for Coil. You also have the weekly 300 Mythology tomestones cap, so you can't gear to iLevel 90 as fast as you would possibly like.

I don't see it as being very wasted, as a lot of people have put it. In fact, if iLevel 80 gear proves to be sufficient enough for Turn 5 later on, I could end up keeping my Mythology tomestones for +1-ing some other Relic weapons I have.