Unless there is a vendor neutral standard for applications you get into the situation where only a few vendors get massive power dictate to everyone (users, developers, manufacturers) the terms in which they get access to the platform.
Now the web isn't perfect but it's the closest thing to a commercially successful vendor neutral software platform in existence.
The vendor neutral standard for Unix-likes is POSIX, and by some extension Windows to the degree it has compatibility, or that it can be bolted on to via Cygwin or whatnot.
Windows itself is a proprietary platform, but it has no central software repository, so developers distribute their software through all sorts of means. Market share means influence on OEMs is exherted, but is it not also the case that if, e.g. Chrome, becomes a dominant browser that they do not exhibit de facto diktat over many aspects of the web?
Android's central platform is Google Play, but you are under no obligation to use it. You may opt for F-Droid or fetching lone APKs.
It seems to me the only platform where central curation is so ingrained that alternatives become impractical, is iOS.
Not to mention the web, despite being ostensibly vendor neutral, comes with a big problem of its own. Now every single page you interact with, no matter how primitive, is behind the scenes potentially a distributed, unobservable, multi-tier networked application with who knows how many layers of caching proxies, CDNs, ad trackers, analytics, data processing pipelines, etc. etc. with no way of knowing what's changing.
Another problem with the web is that every application has a massively different look and feel. I'm not just talking colors here, but some forms validate inputs as they are put it and others don't respond until you hit submit. Etc. There is no common UX for the web and IMO that sucks.
I think you are mistaken -- the web is more consistent that, say, the Windows GUI ever was. Yes, there are small quirks like the one that you describe, but in general, most users don't need to learn how to use a webpage. Have you ever seen a novice wrestle with a native GUI? It's horrific.
POSIX only covers the API's not the ABI's the software will run on. Also, that still leaves them running on a vendor specific CPU architecture.
Your naive if you believe Microsoft and Google don't hold all the cards with thier platforms. More and more of Android is being swallowed up by Google Play Services. Windows does have a central software repository called "Windows Store". Let's not forget about how users have to put up with thier shenanigans because they are the gatekeepers to apps.
Now the web isn't perfect but it's the closest thing to a commercially successful vendor neutral software platform in existence.