It's not about it lagging behind it's about it requiring more special consideration compared to the other big players.
Like styling scroll bars in FireFox. But more often it feels like Safari is the special needs browser.
Sometimes it's because it lags on features. Sometimes it implements a spec differently. Maybe it's the websocket bug of 2021/2022 that took forever to fix(was it?!) because their weird update cycles.
If you're developing for Chrome first, it's hardly surprising that a browser made by a company which takes a much more conservative approach with user privacy and device efficiency isn't going to just adopt every half-baked API the Chrome team throws out there.
Does Safari lack support for some actual standards? Sure. No browser is "feature complete". The difference is, a good chunk of what people complain about, are draft features, made available in Chrome because Google's whole business model is "put everything in a browser, and track the bajeezus out of it".
Like styling scroll bars in FireFox. But more often it feels like Safari is the special needs browser.
Sometimes it's because it lags on features. Sometimes it implements a spec differently. Maybe it's the websocket bug of 2021/2022 that took forever to fix(was it?!) because their weird update cycles.
It all adds up.