Maybe a dumb question, but why can't the regs at least coincide with the general season and be out before it starts?
By far, more citizens participate in lowland lake fisheries than in any other type. Those fisheries are where WDFW makes their hay on license revenues. That makes April (at the end of which the lake season opens) the ideal month to start selling new licenses.
A nice "side benefit" this schedule affords WDFW is that it requires most salmon and steelhead anglers to buy their new license before they know what kind of opportunities they will get to fish for those species (as was mentioned, those seasons don't get set until after North of Falcon). That's good business for the department, because they might have sold a lot fewer licenses and "salmon and steelhead endorsements" in the past couple years had the seasons been set prior to licenses going on sale.
Basically, this strategy maximizes their potential to exploit a shrinking revenue base.