How can that possibly be the case if it's becoming more, not less, standards compliant and performant?!
Additionally, it even manages to outperform Blink in certain use cases / benchmarks, especially after the last major update or so.
It might not be Apple's bread and butter like Blink is for Google, but I see no obvious signs of WebKit dying, though I'm open to proof to the contrary.
I recently lost 2 days troubleshooting an iOS 13 Safari bug: It just froze, when it got certain html. Wasn't possible to connect a debugger. Never seen that in a browser before.
FF, Chrome: all fine, page rendered correctly.
(I had to bisection-comment out half the html page and so on, until I found out what made Safari freeze. The problem: Radio buttons in separate divs but not wrapped in separate forms, killed Safari.)
Depends what you call "actively maintained", I would call it on life support personally, it's lacking very far behind the other engines.