Why are web developers constantly reimplementing native browser functionality? This site for instance has their own scroll implementation that's laggy, adds unwanted smoothing, and of course has less functionality (middle-click scrolling doesn't work, nor does autoscrolling). Fortunately I can get the native implementation by disabling scripts, but I've seen sites that are `overflow: hidden` so you're forced to use their scrolling logic.
There are so many sites now where you can't Ctrl-click, middle-click or right-click links and get proper behavior, where inputs don't work the way they should, where sites try to hijack keyboard shortcuts (and of course assume everyone's using the default ones), where scrolling with the keyboard messes up layouts because they assume you're going to gradually scroll down with a mouse or swipe, where browser extensions can't affect element types because everything is just a <div>, etc.
It's a gigantic pain in the ass for consistent usability across sites, and a complete disaster for accessibility as well.
There's a couple extensions that are supposed to target and disable this behavior, but I've found them flakey at best.