If there's something I hate about Linux, it's CSD (Client-Side Decorations, in case people don't know what it is).
If I wanted all my apps to look different from each other, I'd use macOS. I want a clean desktop environment, with predictable window frames that are customizable and they all look the same. CSD destroys that.
For eons the standard was: the only one with the title bar showing the theme accent color. That is consistent, predictable, keeps the user in the flow.
With CSD each app does whatever inconsistent thing they can fancy. You type and oops deleted something in the wrong window.
Alas now even many default SSD setups fail at this (selected and non-selected windows look pretty much the same) and keyboard-first workflow is much hindered.
KDE favors server-side decorations.
The problem is that sometimes you need to use a GNOME app that looks completely out of place.
Doesn't matter which OS they all have different styles. I can understand it's not liked by everyone, but that ship has sailed and no "big" app will use SSD anymore.