Re: Cross platform development is EASY
Yep a cross-platform UI for kiosks would be straight-forward. Otherwise... not-so-much.
Kiosks are much simpler for such things because the UX is constrained by the very specific nature of the device. But the vast majority of software in the world does not run on kiosks. It runs on various different devices and form factors and operating environments, many of which specifically differentiate themselves from others by differences in the UX.
If cross-platform development was EASY, everyone would be doing it by now and it wouldn't need to be constantly re-invented to get-it-right-this-time-no-honestly-we-have-nailed-it-now. I am guessing you don't remember (perhaps weren't even born at) the time of the likes of Omnis and various other 4GL's that had "nailed" cross-platform development in the 90's - a time when there was far less diversity in platforms to contend with.
Which is of course why Omnis and it's ilk went on to dominate the software development industry and why we are all using those tools now.
Oh, but wait. Then came Java with it's Ultimate Solution to the write-once-run-anywhere problem. Hmmmmm.
Then .NET. Then Qt. Then FireMonkey. Then Xamarin. Then .net Core (Jeez even .NET is taking two bites at the cherry).
It's almost as if this is a bit harder than some people seem to think.