Blizzard took action. At multiple times during classic they restricted xfer onto certain high pop realms, and they offered free xfers to certain low pop realms. No one took them up on the offer to fix these realm populations. They’d just wait until blizzard removed the restriction of xferring onto the mega servers and then they’d transfer there themselves.
Just because blizzard didn’t do what you personally wanted them to do, doesn’t mean they didn’t do anything.