Spotify was never going to have me as a subscriber but Apple Music was so much better (for me) that it was a no-brainer.
But then I always preferred Pandora over Spotify anyhow (different use cases I know, but still).
1. I can add music to my streaming library that is not on their service and that music isn't treated any differently than the stuff in their catalog from a UI standpoint.
2. It integrates better into the Apple ecosystem, which I've already tied myself too. For example, play music using Siri and Apple TV support.
Also, I'm not a fan of Spotify's UI.
2. Spotify works great with Google Now and Chromecast.
Also, I'm not a fan of Apple Music's UI.
I know Apple Music gets hate for it's UI but it's nirvana compared to the horrible, grating, death by 1000 papercuts UI that Spotify has.
So that contributes a LOT to my impression of Spotify.
I find their radio offerings better than Spotify, and the curated playlists to be of higher quality and better variation. The For You tab alone is better than a lot of what I found on Spotify.
The importing of my existing library and linking of it into the service with all sorts of metadata made for a seamless experience that I haven't found from any other service either.
Basically... it's just a little bit better (for me) in every possible way, while being nicer to use.
It happens.
In my opinion, a lot of users of streaming media services are neither enthusiastic customers nor entirely forgetful. Their opinions of the services they pay for aren't consistent from day to day, either.