While you're correct that Unity "solved" the problem, you can't generalize their solution to things other than games. You end up needing a bunch of custom ecosystems for specific problems and when we're talking about enterprise, education, etc apps they often end up needing everything because sometimes you just end up with a massive Our Company's App that has 20 different responsibilities.

To put it another way: Adobe can ship Photoshop using Emscripten, and big companies can probably eventually ship their internal C# business apps using Uno or Blazor, but you're not going to ship either of those using Unity's stock approach without building out all of the platform APIs they stripped out and adding back runtime features that were removed. The decisions they made were perfect for games, but people building general-purpose platforms can't cut all those corners.