I look at Firefox and some of it's inconsistent behaviours around flexbox compared to other browsers (mind you, some of these are due to the spec). Just today I had an irritating render bug in Chrome.
I know, this all comes down to hearsay and individual experiences. But I still strongly believe that 'Safari is the new IE' is nothing but baseless FUD.
Regardless, that's not the point. I'm not saying that Safari is perfect, I'm just saying that while it might have some implementation differences and bugs, so do other browsers.
(only kidding, but it's not the most obvious thing to check and optimize for if you're a web dev. If that's what Safari's problems are, it's pretty solid.)
Im also a Safari user, and in the majority of cases the reason it is not supported is because the page/app uses some custom Chrome-only, non-standard feature. Like this one.
Granted, this is more of a flexbox spec issue (last time I checked this behaviour is intentionally undefined), but it's still an annoying case of one browser doing something all the others don't.
"Widevine, a Google company" sounds neither standard nor very open to me: http://www.widevine.com/
But... safari is now the one that has weird behaviour that does not occur in Firefox, chrome and edge. Just because historically there was a massive split in behaviour doesn't mean that Safari gets off free. It's the one browser I hate testing because there are usually edge case and unexpected behaviour.