There are two issues here: seasonal award requirements and capacity controls. They are totally separate.

A coach MileSaver award is either 60,000 or 40,000 miles, seasonally based.

A J MileSaver award is 90,000 miles no matter what time of year it is.

All awards have capacity controls. They can be waived for 2x the miles.

If you want a coach award in low season and all the MileSaver seats on a flight are gone (but there are still seats on the plane) it takes 80K miles to waive the controls. In high season, 120K. In J, 180K year-round.

As noted, flights where AA expects higher demand for paid tickets have lower MileSaver award availability. To some degree this is related to seasonality, since demand is the basis of both, but it's influenced by other factors (such as day of the week) as well and can be adjusted flight by flight as AA tracks demand for each one individually.

So, if you want to fly when everyone else does, get in line early and be flexible.