I should say it's not even specifically developers, it's just a broad assumption in the industry that people want things "fancy", that animations and loading and switching and so forth can take longer than .5 seconds because "people don't notice".
Every company developing apps only thinks about themselves and the OS they interact with, at most they'll include some share function, but OS-native theming? Multitasking performance?

The result is a slow piece of shit, that looks like a circus tent🎪

I have seen people use computers fast, except in all cases it was some kind of specialized software and no mice. Mostly in retail.

One example stuck in my head in particular is the information system in a chain of hardware stores in my city. The thing runs in text mode and is fully controllable with a keyboard. It must be fast-usable because there's no feedback required at all — after you've used this system for a while, you develop a mental model of its states and how it transitions between them. You don't need to constantly look at the screen to make sure the program is in the state you expect. You just enter the sequence of keystrokes that are required to get it from its current state to your desired one, without paying attention to the intermediate states.

Various kinds of forms work like that too. You build a mental model of the form and then you tab through the fields without looking at the screen.

And POS systems. Cashiers and waiters are often extremely fast at ringing up orders. It's often touchscreens these days but muscle memory works with touchscreens too.