I wonder if people will choose not to buy games developed in Unity after all this backlash?

There will always be people who make those choices, but the majority of players don't shop on engine.

Also, the engine is rarely advertised, so most of the time you know after the fact.

There's actually a somewhat curious detail about this - Unity doesn't allow you to remove the Unity logo when using the free (Personal IIRC) license for your game. This has led to people sometimes associating Unity with bad games, because if a game shows a Unity logo it's probably not the highest quality, especially considering all the asset-flip games. There's a lot of big Unity games whose developers obviously paid for the engine, so you either see the studio's logo or just a loading screen.