He's a dick. Got paid already, it's the last year of his 4y contract, almost $20M base.
Why not play it out and get paid again next year?
So in general I agree with the premise, which is why most of the public is "against him" in this holdout. However, two things I'd point out, which is likely his thought process:
1. He's the 7th highest paid DT in terms of cash compensation this year. That's not dreadful, but I imagine he thinks he should be closer to the top.
2. He has no gtd $ left on his contract, and no additional years on his deal beyond this one.
I imagine the latter is the biggest sticking point. He wants long term job protection, and he wants as much $ now as he can get it. Like yeah, if he has another great year, he'll get a huge deal in 7 months. But if he gets hurt, he'll also get a much lower deal in 7 months.
Would also point out that him getting franchise tagged next year is an option, and that # is projected at ~$21M today. So if he doesn't get an extension now, he risks getting paid below market value (and one a one year deal) again next year. And honestly, the FT makes plenty of sense for KC, because it'll be like $7M less than his cap number for this year (currently at $28.3M).
It's not super clear what he would get in AAV as a FA, but I would imagine the 4 year, $96M deal the Jets just gave Quinnen Williams is at least the floor for discussions. He may not get a 4 year deal, but in AAV it'll at least be that much.