It's very hard to actually write good UX from scratch, particularly stuff like scrollbars that require all sorts of relative resizing, drag listeners, velocity methods, second and tertiary controls (keyboards, drag-selection of text) and often need to handle those things after a variety of user interactions without redrawing their content or slowing anything down by constantly remeasuring the rest of the UI.
Because it's difficult, it's often done poorly, which leads to people thinking it should never be done at all.
To your point about games, I find most custom-written scrollboxes in games to be pretty terrible, but we all kind of appreciate them just for their uniqueness, because as UX items they're generally not something you interact with that much. (Unless you're playing Crusader Kings, in which case ... )
I remember being disgusted and offended by Apple's app developer rules two decades ago, which included dictates such as never implementing your own UX elements like scrollbars. We're still debating whether they were wrong. As long as there are bad ways to build UX elements, some people will do them, and this will serve as proof for a few big companies that it should never be done.
You don't have to write good UX from scratch to get non-OS scrollbars, there are CSS rules that let you style scrollbars while keeping most system scrollbar features and accessibility.
No comment on whether or not that's a good idea, though.
I think in games reimplementing controls is done because of game engines having their own gaming-specific widgets or parts, which are not using the system's widgets themselves. Game creators will make use of the things available in the game engines.
Well like e.g. when I had to write UI elements into first iterations of Star Citizen, those were all in a 2D vector/sprite layer over the 3D world that had to be completely custom coded. Even the shape of the UI was pretty much completely open to interpretation. I have mad respect for people who write their own UI elements and "widgets" into games, given the restrictions that are often involved. Some do it better than others, but therein lies the art of observing and stealing from the best.
Because it's difficult, it's often done poorly, which leads to people thinking it should never be done at all.
To your point about games, I find most custom-written scrollboxes in games to be pretty terrible, but we all kind of appreciate them just for their uniqueness, because as UX items they're generally not something you interact with that much. (Unless you're playing Crusader Kings, in which case ... )
I remember being disgusted and offended by Apple's app developer rules two decades ago, which included dictates such as never implementing your own UX elements like scrollbars. We're still debating whether they were wrong. As long as there are bad ways to build UX elements, some people will do them, and this will serve as proof for a few big companies that it should never be done.