"can’t that time be spent instead on making desktop apps as sandboxed, OS compatible, easy to download and execute as web pages"It can! This is (sort of) the vision of my current company [1]. Its founding belief is that web tech is reaching end of life and it's time for our industry to start looking at what comes next. The long term goal is to create a new competitor to the web, but not all at once. Instead we're doing it via incremental iteration on current desktop development. Starting with better distribution tools we want to work up to sandboxed, streamed, cached, crawl-able, embeddable app/document hybrids just like the web has but with very different architectures that benefit from what we've learned from 30 years of the web.
The starting point is to make it as easy for people writing desktop software to distribute their work cross-platform as it is for people making static websites. The resulting UX is that of a normal desktop app as far as the user is concerned but from the developers perspective they just grab the tool we've made and run "conveyor make site". Out pops a set of files you can upload to any static HTTP server, which are fully signed, notarized and self updating for every desktop OS. It can do this because all the packaging and signing code is implemented by the tool itself, so there are no native dependencies and it can thus be very convenient to use.
For people who like the React model an interesting way to use this is to write an app using Jetpack Compose [2] for Desktop [3]. You get a fully functional/reactive UI toolkit but without needing a mishmash of HTML/CSS/JS - it's all just Kotlin. Your Android code can be shared directly with the desktop version (with layouts for larger screens of course), and you can then go ahead and start integrating with native OS capabilities as you see fit by directly invoking their APIs. For "mobile first" companies that develop a web version primarily for desktop users, this can eliminate the need to build a web app entirely (or you can use a minimal one for search engines). Next week we'll be releasing an update that improves support for Compose Desktop apps, in fact.
There's more work to do on making distribution trivial for everyone, and of course you can use Conveyor with Electron apps if you want to - the goal here is to be layered so the lower levels are usable by everyone including web developers, and the platform gets incrementally more opinionated as you go up the layers. Once the core product has matured further we'll be exploring an experimental architecture in which RDBMS' fully replace the web server, and what advantages you get from doing so.
[1] https://hydraulic.software/
[2] https://developer.android.com/jetpack/compose
[3] https://www.jetbrains.com/lp/compose-desktop/