I think NHL GMs have been aware of Zegras' availability for quite a while, so if anybody was lining up to make better offers, they had lots of time.
Of course it probably also means Anaheim has a line on some huge UFA signings. With Joel Quenneville hired and almost $40M Cap space it has been expected they'll be going after a couple of the biggest UFAs, probably Ekblad, maybe Marner too. And this is probably well within the "collusion" window for teams lining up their contract announcements for July 1st. Maybe they already know who they have coming in and that made them more ready to firesale Zegras than previously.