I personally don't think this is "the problem". Every platform has more than one UI library: on macOS you have AppKit, UIKit and SwiftUI. Windows seems like the worst offender with WinUI, WinForms, WPF, Blazor, .NET MAUI, etc [1].
I do think it's just a incentive issue. Supporting a platform on React Native takes plenty of effort, so without a big app as both the motivation and test-bed figuring this out there's little reason to invest in it.
Every platform has more than one UI library but there's two (closely related) fundamental differences:
1) there's typically just one canonically recommended for a given use case at a given time
2) they tend to a better job interoperating with one another & conforming to a consistent desktop paradigm than popular Linux equivalents (see e.g. running qt apps under gnome)
This is all largely because they come from singular entities - achieving the above would require more effort & coordination from Linux folk (though KDE do a decent attempt - Gnome has a lot to answer for here).
I do think it's just a incentive issue. Supporting a platform on React Native takes plenty of effort, so without a big app as both the motivation and test-bed figuring this out there's little reason to invest in it.
[1]: Not really a reference, but just a thread with people's thoughts on this whole mess: https://www.reddit.com/r/csharp/comments/vc3e2l/winui_3_or_w...