It's wild to me that those managers would have been loyal enough to the company to behave that way toward you when not only were they themselves on the way out

It's wild to me that those managers would have been loyal enough to the company to behave that way toward you when not only were they themselves on the way out the door, but the hypocrisy of it would have been instantly obvious, on a timespan of days, not even months or years. My impression is that in the modern world, most workers consider their personal network to be of much greater value than any ways that their current employer could reward them for "loyalty". Having been a manager and had people quit on me, my response has always been pretty candid and along the lines of, "yeah, obviously this is tough for me as I've really valued your contributions over the time we've worked together. However, you've been clear about your expectations as far as comp/projects/tech/mentorship/career/whatever, and although we've tried to do what we can, I can understand that the role is no longer a great fit for you, so the decision to move on makes perfect sense. Best wishes with your next gig."