These core users (indie developers) aren't "convinced" anymore, they're starting to be skeptical of Unity's management of their engine. Since Unity has failed to fix so many bugs and left too many half-faked features abandoned, they are starting to think Unreal is a much more stable choice in the long term. Gamedevs value engine stability and workflow improvements far more than just shiny graphics and new features, because at the end of the day the most important thing is how you can actually ship a game without problems, not how it would look good in trailers.

Also, Unreal has enough money to burn (from Fortnite) to venture off into new spaces. Unity is taking far more of a risk here, since these indie gamedevs are still the main revenue flow (especially considering that Unity sells their engine in a monthly seat-based system rather than a revenue sharing model like Unreal). If these core users move away and investors become skeptical that Unity's going to make money (they're still burning tons of investor money every year without significant revenue), what we're going to see is a total disaster.