Note that Wimmer has two years of remaining eligibility - so even though he'll be playing as a "senior" in 2023, he'll still have leverage in the draft.
I think it's safe to say they didn't offer him what he considered enough. They presumably offered him $175k or so - the max they could, given the bonuses they paid higher picks. They presumably held off signing Karaffa until this morning, waiting to see whether Wimmer changed his mind or not.
It will be interesting to see if Karaffa's bonus exceeds $125k.