Apparently these libraries and the languages they are designed to be used with failed to offer sufficiently easy way to implement the UX people want.
I myself strongly prefer classic desktop GUIs adhering to the 90s Microsoft and Apple design guidelines, also well-designed (rather than chaotically evolved like JavaScript) programming languages too yet the objective reality seems like that's not what the demand is for - real-life companies and people prefer fast-entry non-proprietary languages like JavaScript and virtually-unlimited expression like what CSS gives. The only libraries I know can technically be good alternatives to Electron are Qt Quick, WPF (and its spinoffs) and JavaFX but they all have downsides which limit their adoption.
Because it's a wrong approach to a problem that was solved decades ago by much smaller and faster system libraries for UI development.