As a user, I want common UI controls to look and behave the same way across all web sites. Ideally, across all applications on my OS, but that's also a lost cause. POLA[1]. I can accept if the developer wants to somehow extend an existing control to support something new, but it's so irritating when they just re-implement their own thing entirely because they think their ideas are better than the browser's. Multiply that mentality by every site out there, and you have the web as it is today: Everyone's site looks and feels inconsistent with every other site. And everyone ships a different 500 lines of code, each with different bugs, just to implement a drop-down box.
This is one of these things that sounds perfectly logical -- you want all UI components to look and behave the same across all applications and all websites -- but that is more theoretical than practical.
If you built an app that used just what the browser gives you and nothing more, you're leaving so much functionality on the floor. Having more expressive power often makes things simpler -- using more complex UI controls has allowed me to eliminate whole pages from my application. Users are happier and more productive.
Browser UI implementations can't do one thing that is vital: compete.
With this kind of take - why do we need different applications at all?
UX/UI is solved just use spreadsheet grid, you can do everything in spreadsheet and you will have exactly the same interface/way of doing things.
It is not a joke - I personally have like 80% of things in a spreadsheet (don't get me started what kind of spreadsheet abuse I have seen in my career). But I do understand that lots of stuff can be done much more efficiently with tailored controls and not everything is couple of drop-downs/text boxes.
1: https://en.wikipedia.org/wiki/Principle_of_least_astonishmen...