It shouldn’t be. We never want to build the same app multiple times. What I (as a developer) want is for OS companies to stop with all the proprietary crap and cooperate so I can write an app once. Web apps and web-as-native (and previously, cross platform GUI frameworks) are our reaction to this lack of cooperation.

See also: compilers, libraries, ORMs, autotools, Docker, ... We as an industry go to extreme lengths to work around crap that’s incompatible for no good reason.

It's incompatiable for a good reason, the reasons just don't benefit us. It makes Windows/various vendors extremely wealthy to have bizarre lock in arrangements.