I would love for the HQ to move back to Seattle but this would send a signal that they put their focus on the commercial side of things. And although it has generated the most revenue ($36 billion as opposed to $24 billion for Defense and $18 billion for Global Services in 2023) Boeing doesn't want to be identified as a commercial planemaker only. Plus, I doubt the state of Washington can provide the company the kind of tax incentives Illinois has or will continue to.
Washington gave Boeing $86 million in tax breaks in 2022; as near as I can quickly find Illinois tax breaks totaled about $65 million in total, not per year.
Boeing has since moved it headquarters to Washington D.C.