A robust cross-platform ecosystem for the underlying programming language is a necessary but insufficient piece of the puzzle.
Given the proliferation of HTML and WebView/web-tech wrappers (Electron, Tauri, React Native etc.) there are now enough "good enough" solutions that most organizations that would underwrite the in-house R&D of a new Neuron Data or Delphi or Flash simply don't feel the need.
When it does happen — say Google Flutter — it's almost statistically impossible to keep the hydra of VPs and biz folks aligned over the decades of ongoing investment it takes to mature & form community around this kind of technology — see the recent Flutter team layoffs at Google.
[0] speaking from my experience building a cross-platform GUI solution in Rust for several years now; see pax.dev