It's not just about safari not adding support for new APIs, but intentionally breaking old APIs. A lot of websites that used to work on safari no longer work, due to their war on tracking and advertising.
Say you are in myCity.gov and you have a website that loads dashboards. These dashboards are iframes that come from anotherDomain.gov, thirdDomain.gov. Well, in Safari they're not going to load because iframes no longer send cookies back to their parent origin unless the iframes are a subdomain of the parent domain. They just broke a thirty year old web standard. That's a massive breaking change introduced by Safari, that makes many corporate intranets and cloud-based delivery sites not load properly in safari. And has nothing to do with not supporting a new vibration API. This is basic old school web semantics that Safari has been breaking right and left because they can't conceive of the internet as anything other than a content-marketing platform.
The web is now used for pretty much everything, and large swathes of it don't load properly on Safari. They don't care, because people mostly use Chrome on the desktop and Safari on their phones, and people have come to expect apps for the content delivery on phones. But this drives the bifurcation further, and solidifies the chrome-only nature of many websites because they are not going to remap their domains to something Safari will approve of in order to get iframes to load properly.