Yep. The insanity of thinking you could apply it retroactively to already licensed games was absurd.
If you tied it to a future main version release with features people wanted, you could absolutely get away with some light pushback that's the usual grumbling on price changes, and a lot of developers would suck it up and move to the up to date engine anyways.
But when you try to pull the rug on people for stuff they've already been developing under previous terms, they're going to seriously reconsider, and on stuff they already published makes it extremely hard to justify working with you again.