I really wonder what really causes it.
Edit: This may help: https://www.mozilla.org/en-US/firefox/new/
My main issue, FWIW, is not that Apple don't fix bugs - it's the long timeframes they take between releases!
As another for-example, I was able to hard-crash safari on ios by setting some CSS attributes on the scroll track about eight months ago - like literally a web page with css that altered how wide the scroll bar track was could CTD safari on ios.
As another for-example, KeyboardEvent.key isn't supported in safari.
As another for-example, http://caniuse.com/#compare=chrome+51,safari+9.1,ios_saf+9.3 and scroll down. Battery Status API, Fetch API, Proxy Objects, Shared Web Workers, on and on. The "modern" web as a good platform for interesting progressive apps is passing safari, in particular iOS users, by.
One assumes a motivator here is the app store: apple's walled garden approach is fundamentally incompatible with web apps gaining all these APIs, whereas android's (relative) openness means Google is less uptight about people deploying apps without going through the app store approval process.
I use Chrome for work and Safari for casual browsing. Safari definitely has better tab management (tab expose). I am also sad that Firefox UI looks stale. Their settings & options window look like it hasn't changed since initial release.
Worse, it wasn't something fancy that it's understandable isn't supported in older browsers - it was scrolling, something that literally every web browser ever has been able to do.
Finally, as a web developer and as someone that has used Safari as his primary browser for many years, I rarely have an issue with Safari being "buggy and inferior". You may not get cool new APIs first, but Safari is usually pretty solid and bug-free with the ones it does support.
Funny you use that phrase, because that's what Google expects me to invest to use their bloated excuse of a browser.
I mainly use Safari since it has such a performant UI that doesn't chew up battery-intensive CPU cycles all the time.