Alaska Airlines Mileage Plan - F Bookings on mid-cons, seems busy...

I'm booked in First, courtesy of a flexible corporate travel policy (fare is "close enough" to the coach fare to allow purchase into F cabin based on total #s flown) and I'm once again noticing that my cabin on ORD-SEA, nearly 3 weeks out, is almost full (4 open seats). I recall this being the same situation on my last trip nearly 2 months ago and the same timeline. I checked American, and a large # of their first class seats seem booked on the same day, while United - not so much.

I'm just wondering if people are indeed booking more and more revenue F or does Alaska have some pretty liberal mileage-upgrade opportunities? (i've never used miles on AS to sit up front..)

Or does this route just get a lot of travelers who will fork out the $$$ for up front vs coach?

I think that your situation may hit on one of the reasons: the price differential. I just booked ORD in early August and the lowest economy fare for the day I needed to travel of ~$330 o/w was instantly upgradeable for me as a Gold. I was surprised U space was available as I've found it historically fairly difficult on the ORD route (mileage upgrades would also come from U). So it could well be advance upgrades, either MVP/Gold or mileage.

AA has a promotional F fare of a little over $400 o/w which might be driving some bookings their way.

A long shot and probably not large volume, but could cruise traffic (possibly bulk or discounted) be contributing to it too?