So what changed between the time leading up to thargoids openly attacking stations and when it happened that no such escape by the elites or anyone else seems to be priority?
I suspect primarily "the development of the FSD".
At the time Project Dynasty was being implemented, interstellar travel even over relatively short distances was a slow process, exploration to the distances they went to (barely over 10kLY) was virtually unheard of, and moving even a few millions of people out of the way of a Thargoid invasion would need decades of advance preparation to get the infrastructure in place.
Following the development of the FSD multiple things have changed to make the project in its original form obsolete:
1) You could move a few million people
and a decent amount of infrastructure to the other side of the galaxy in a matter of weeks with merely "regional power" levels of resources (the Colonia Bridge project essentially
is) - a superpower could probably move tens of millions.
2) The expansion of exploration has made it clear just how many ELWs are out there - especially in the denser areas towards the galactic core which were outside their effective range back then - and therefore there's really no need to terraform anywhere, certainly not decades in advance of your arrival.
3) If you start visibly running away from the Thargoids
too soon you're leaving behind an intact bubble who purely by weight of numbers may be able to locate, invade and capture your bolthole, killing you and taking it for themselves. You can't actually flee until by the time people have realised you're gone and have left them to their fate, they're too busy dying to go after you. And therefore you
still have to keep even the possibility that you could do that a complete secret. (pre-FSD you could have fled years in advance of the final disaster and still had pretty good odds that no-one would figure out exactly which way you went, as well as having the firepower to destroy anyone who did before they escaped again)
(They probably
are still preparing secret boltholes in terms of quiet supply caches outside the bubble, but that's all they need to do right now.)
As for non-elites escaping, Colonia took in a substantial number of refugees when the Thargoids were regularly raiding the bubble itself. Since then ... well, Thargoid attacks on the bubble have been rare, fleeing even to Colonia is going to be difficult and expensive for most, the elites are partying at Jokers Deck rather than running for their lives ... how bad can it be?