I earnestly don't care about the actual 'season', and presumably that's why the devs aren't keeping it sequential, as a season lasts ~12 weeks and they presumably have 'new' content due in ~24 weeks (or ~36 weeks from the end of Season 4), and 48 weeks would be 'too long of a wait'. However, I *do* care about playable content that's been added to the game, that I'm literally unable to access despite owning the expansion just because it's 'not the *correct* season'.
What possible harm could there be in allowing a user to restart a manhunt from a previous season? Allowing one to restart the current manhunt and/or unlock the finale mission of all 4 manhunts through seasonal progression is nice 'n all, but falls a bit short in this case.