Laptops and smartphones are made for doing different kinds of things. The real-estate requirements are different, as are the typical use cases, and even in the case where you solve them both with, for example, dynamic web pages, you still end up coding for both use cases separately, you just now have it all stuffed into the same codebase, which is harder in many cases instead of easier.
I believe Microsoft has been trying to make all OS usecases the same for decades. I believe they have not succeeded, not because Microsoft is deficient somehow, but rather because it's not, fundamentally, a good idea.
I think that dream is possible with OS usecases as well, it's just that nobody has made it work yet. And I can't think of a better way to eventually get there than to build it slowly out of free and open source software. It might take a while, but since people have the ability to adapt the software to their needs when it is free, I'm confident with time that it will serve those needs.
I think part of the motivation was also managers thinking they could easily shuttle developers between frontend, backend, and database work, and that has mostly not worked out, because what takes time to learn about each is not the language, it's the problem space and the tradeoffs.
But, if it's working out for you, I'm glad it is. I was not impressed.