I can built a basic app with html, javascript, etc that supports many platforms in an evening. How long do you think it would take to support windows, macos, ios, android, xbox, linux, etc, etc? Much more than 50x the time even if you already are familiar with development on all the plaforms.

Qt covers 5 of the 6 platforms you named, and many more "etc".

Yes it takes a bit more than a boot camp graduate to code that, and might take a bit more time still.

See?

Your solution requires more dev time and skill - which makes it way more expensive. Basic economics.

The main requirement most devs and users have for an app - that it runs and works reliable. Not that it is the most efficient solution.

It's the same in any other industry where cheap plastic overtakes all, except and average user can't tell the difference, other than on "my PC is slow" level.

It is everyone's responsibility to not make shit software.

5 of the 6 isn't a fair comparison

Flutter or React Native are also easy to develop with and cross-platform, no need to learn C/C++.