[Zak]

I have no doubt marketing played a role, but Chrome and Chromium-based browsers were the only ones with a multi-process architecture for over half a decade after Chrome's launch. That meant a bad web page couldn't crash the browser or block the UI, which used to happen frequently on other browsers.

Firefox eventually caught up, but had lost much of its userbase and mindshare by that point.

[jwells89]

WebKit went multiprocess with the release of WebKit2 around 14 years ago, with the difference being that the multiprocess architecture is part of WebKit itself and thus easily reusable — just embed a WebView in your app and you have it. This contrasts to the Chromium implementation where multiprocess is handled by Chromium rather than Blink, meaning to get multiprocess you have to ship the whole of Chromium and can’t just embed Blink.

That said this really only relevant for Apple platforms and Linux/Android, unfortunately. WebKit for Windows is somewhat in a state of disrepair.