So many things were making it slowly less and less viable through extra costs/requirements would've likely been the better plan, but instead nothing changes until at some point there is enough pressure for change, and then there's complaints its "so suddenly". (I think with Avgas that has happened a tiny bit through storage regulations - its sufficiently more annoying to keep around that some places don't offer it anymore, making it a tiny bit less attractive for plane buyers)

Then people will just complain it's sudden when it gets close to the deadline.