I doubt that .NET has much to do with it. There are just many more JavaScript developers who know how to make UIs.
While they do their best to open source .NET and related SDK tooling, the whole IDE story has been a bit of a mess, rewriting VS4Mac only to kill it shortly after the rewrite reached 1.0, C# DevKit under the same license as VS, the stuff that will never leave Windows or VS to Mac/Linux, Xamarin.Forms rewrite, while not taking GNU/Linux into consideration, and using Catalyst for macOS MAUI backend, dotnet watch drama, some of the ASP.NET features seen as way to sell Azure stuff,....
If you look closer, you will notice that usually the React Native or Electron based applications are from business units that are mostly C++ focused, that never had great love for .NET in first place.
While the team tries to cater to new generations with making .NET development a great experience, even with some constraints in cross-platform deployments, I think they would gain more by fixing the bad perception .NET still gets in UNIX shops, which those upper management decisions don't make any better, regardless of how great .NET happens to be.