I've been using Swift for production work since shortly after it was released (much of it on an internal enterprise application which is how we were able to start using it right away).
What makes Swift really nice to use in its own right is that it has a lot of useful language features (like closures, generics, tuples, etc) with a syntax that can be kind of boiled away to the degree that you choose, to keep code clear and understandable. I think the best way I could describe it, is that it's like a functional language buy is very practical and doesn't get preachy about it.
So already the language is very pleasant to use. The real benefit Swift enjoys that give it such a high rating though, is that it comes with very advanced tooling and a super-integrated mirror-counterpart language (Objective-C) right out of the box.
Think about it, how many new languages like Rust suffer because you have to build up syntax highlighting support in the editors you like, figure out a new build process tailored to that language, how to run the applications and so on. With Swift if you knew XCode you could easily just start writing Swift and all of the annoying overhead was gone. Even if you DIDN'T know XCode, at least it's a pretty advanced tool dedicated to helping produce running code in very short order (VERY short order with Playgrounds).
Then along with that, you have a new language which invariably has some missing features or capabilities, that make some particular thing you are trying to do hard in the new language. Well in those cases, Objective-C is very close at hand - you can mix code from both languages easily in the same class even. For example Swift itself is strongly typed and has very few reflection or dynamic method lookup features yet. Objective-C is kind of the opposite way, full of dynamism and runtime reflective use, so you can jump over to those abilities as needed.
I don't think people outside the iOS community realize just how fast everyone doing iOS development is switching to Swift. Swift (for me) has actually worked really well since day1, the tooling was rough for a while (with the syntax highlighter/code completion crapping out regularily on Swift code) but I THINK it may finally be OK.
It's definitely not a case of people hating Objective-C, because a lot of the people that like Swift also liked Objective-C. It's a case of having some good tools already, and being given another tool that seems to work really well for some tasks and thus appreciating having an expanded toolbox...