WebKit does build on Windows, and it's possible to use bare WebKit: https://schepp.dev/posts/running-webkit-on-windows/
But there is for every other OS.
Macs can use Safari, obviously.
On Linux, KDE users (or other Qt based desktops) can use Falkon, and GNOME users (or other GTK based desktops) can use GNOME Web.
Webkit browsers in linux feel a bit half baked as well, though, when you compare it against Firefox and Chromium.
They're just browsers. They don't have built-in web services, they don't dial home, they don't sync your history and bookmarks with some unknown service. Frankly, this is a positive.
I miss cosmetic filters from µBO and should implement something like Privacy Redirect, but vertical tabs work more easily (they don’t require hacking around user.css to disable horizontal ones, though there are no tree-style ones), there’s a simple Stylus alternative, userscript support, JS whitelisting/toggling with a modifier-free binding, and of course native vi/Pentadactyl-like bindings which make extension-provided ones feel viscerally painful (they’re not eviscerated whenever a page is in the process of loading or unloadable, and searching stays incremental).
They also removed many useful features and hide useful settings... (one example being the RSS feed finding feature .... luckily there's an addon that you can install that does a pretty good job, it is called Awesome RSS)
I do use Firefox, but Mozilla really goes out of their way to betray their core audience more and more with addons like Pocket being integrated into the browser along with advertisements in the new tab window.
In either case it always feels like no matter what browser I'm using there are huge tradeoffs in one sense or another, which I never felt when I originally started using Firefox early on or early Chrome.