Everything is a trade-off. If, as a developer, you have to spend ungodly hours on learning multiple UIs, you will have less time left for the actual business logic of your app. Which, from the user's side, means one of the following three:
a) nice looking, but less capable apps,
b) more expensive apps, or, apps that have to be paid even if they could be free in an alternate universe,
c) limited availability - app X only exists for Windows and not Mac, because either a Mac programmer isn't available or would be too expensive.
Developing for multiple UIs at once is both prone to errors and more expensive, you wind up paying for extra developers, extra testers/QA, extra hardware and possibly extra IDEs and various fees. Such extra cost may be negligible for Google, but is absolutely a factor for small software houses outside the richest countries, much more so for "one person shows" and various underfunded OSS projects.
I remember the hell that was Nokia Series 60 and 90 programming. Nokia churned out a deluge of devices that theoretically shared the same OS, but they had so many device-specific quirks and oddities on the UI level that you spent most of the time fighting with (bad) emulators of devices you could not afford to buy. This is the other extreme and I am happy that it seems to be gone forever.
If your application can be useful on different OSes (and now there are only 3 OSes in existence, as porting Desktop application on Mobile requires completely different UI and UX no matter what technology you use!), break it into business logic and UI and find partner or hire developer who love to develop native UIs for other OS. MVC pattern is old and well known (though not fashionable now, I understand).
OSS projects are completely different story, of course, no questions to OSS developers.
I prefer to pay $200 for native application than $100 for Electron one.
Oh, whom do I try to fool? Of course, it will be Electron app with $9.95/month subscription now :-(
"break it into business logic and UI and find partner or hire developer who love to develop native UIs for other OS"
As I said in my previous comment, this is quite expensive, and people inside Silicon Valley rarely understand how cash-strapped the software sector in the rest of the world is. In Czech, we have a saying "a person who is fed won't believe a hungry one" and SV veterans that are used to reams of VC cash supporting even lossy businesses like Uber have no idea that the excess spending needed to hire another developer for several months somewhere in Warsaw or Bucharest may kill a fledgling or small company.
a) nice looking, but less capable apps,
b) more expensive apps, or, apps that have to be paid even if they could be free in an alternate universe,
c) limited availability - app X only exists for Windows and not Mac, because either a Mac programmer isn't available or would be too expensive.
Developing for multiple UIs at once is both prone to errors and more expensive, you wind up paying for extra developers, extra testers/QA, extra hardware and possibly extra IDEs and various fees. Such extra cost may be negligible for Google, but is absolutely a factor for small software houses outside the richest countries, much more so for "one person shows" and various underfunded OSS projects.
I remember the hell that was Nokia Series 60 and 90 programming. Nokia churned out a deluge of devices that theoretically shared the same OS, but they had so many device-specific quirks and oddities on the UI level that you spent most of the time fighting with (bad) emulators of devices you could not afford to buy. This is the other extreme and I am happy that it seems to be gone forever.