Let me guess, you use iOS? Play Music and Spotify both integrate roughly equally poorly with Google Now/Assistant. You can say "play some X", and it'll ask you which you want to use the first time.
Unless it misinterprets which you wanted to use, which happens 90% of the time for me. It consistently interpreted "Movits!" as "Movies", even despite having their whole discography favourited in both Play and Spotify.
And that's a good thing given the fact that Google Music (like most Google services that are not free) is only available in the US and a handful of other countries.
And Google's/Spotify's problem is that they do not have any good or even decent phones.
The problem is that digital music is a type of good that is mispriced by the free market: a public good. There needs to be just enough money to going to the artist to get the album recorded, and once that amount of money is there, there is no incentive for anyone to give more money. Giving more money won't make it easier for more people to get the music, because distributing it digitally is pretty easy/cheap. Kind of like a public park. Because this incentive is only there up to a point, the good gets mispriced.
My second biggest annoyance is the increasing trend of "artist exclusives" if you pay a monthly fee and your favorite artist are giving exclusives to the other services I'm less inclined to continue using that service(Spotify) because I don't get the content I want. I don't want to pay for 2 or 3 streaming services. That fracturing of availability is more likely to people going back to pirating music in my opinion.