I don't know anything about you, but I'm gonna hazard a guess and say that like me you're not a millionaire. But I imagine, in whatever line of work you are in, you keep an eye on what you are paid and the benefits offered by your employer in relation to other similar jobs and companies.
I agree with you on pure principal, but in practice why would anyone deny themselves a pay off that, at least by the standards of their industry, they believe themselves to be owed?
Dyche "earned" his coin much more than Lampard, Benitez, Allardyce and Silva did.