It solves a _development_ problem, in that it reduces the amount of work needed to allow an application to reach a larger number of devices. Basically the same reason for things like React Native and PWAs.
> Ubuntu tried this - how'd that go?
So because someone else failed at solving a particular problem in a particular way previously, we should simply give up on it?
Sounds like a repeat of the Java strategy: you can run garbage nobody wants anywhere nobody wants to run it.
> So because someone else failed at solving a particular problem in a particular way previously
Microsoft also attempted it, and also failed quite miserably.
> we should simply give up on it?
Not necessarily, but at the very least you could avoid lying by omission (mentioning Google and Apple which don't exactly attempt convergence and pointedly ignoring every pre-existing attempt at the concept) and maybe consider humility and avoid overblown claims given you're not the first to attempt it, nobody's succeeded, there's no evidence available that you are succeeding, and you've really not shown anything which would made anyone think "this is going to succeed where everybody else failed".
I think the GP meant to ask "what problem does this solve for end users?" It's hard to market to consumers if your primary differentiator is only useful to developers.
The reality is, if a developer can generate greater reach, it gives more options to the consumer. And so in that regard it does solve a problem for the end user - they have more software options to choose from. Perhaps there is more competition, which I think we can all probably agree is good for users.
That's great for developers, but how does that help users? As a user, I would rather use something built specifically for the device (and os) I'm using, I've used enough things that were supposed to work everywhere that it's a major turn off at this point.
If developers want to share code cross platform, really, the way to do it is write a shared core logic (probably in C, because that is available everywhere), and then write the UI from scratch everywhere, conforming to the platform guidelines (unless it's a media player). It's more work than hoping a write once run eveywhere will work well, but it delivers a much better result.
It helps users by providing apps.
Purism phone is very niche product. It is unreasonable to think that a lot of developers will start writing their application for PureOS. But hopefully some of them can port app if it will be easy enough. So instead of OS without almost any apps you will have OS with some apps.
My laptop is where I do all of my serious computing. I have no desire to run bash or vim or tmux on my phone.
Having been a user of Windows Phone, I would say, don't bother giving me an app if it's going to be garbage.
But if the cost of doing so is that the apps have to be mediocre, is that really good?