The first thing that comes to mind is that all of my desktop development for the last few decades allowed a solution to be programmed in a single language (say,

The first thing that comes to mind is that all of my desktop development for the last few decades allowed a solution to be programmed in a single language (say, C), using a straightforward display model (an X,Y screen), all talking to an operating system, whereas web programming is anchored in a multi-language situation (HTML, CSS, javascript) with a rather complicated document-object model, all living in a web browser. Neither approach is easily reconciled with the other, and so the two techniques have little hope of merging. Personally, I hope the popularity of programs running essentially standalone on phones drives away the expectation of using a browser to host programs, and the idea of forcing everything into a web browser dies away.