Google seems to be caught in an awful feedback loop. I feel like at this point, most tech savy people are weary to try new Google services for fear of liking them, but eventually getting shutdown. In turn causing those tech savy users to not recommend it to their friends/family that actually might cause it to grow.
Honestly don't know how they get out it without either losing tons of money on maybe side projects or happening across the one things that's so good it's impossible to not use. The latter seems more unlikely by the day
Ehh, I'm sure it's something like if they let you manage your subscription through the play store, Google is entitled to their 30% cut. If you subscribe through desktop, they'd like to keep 100% of the money opposed to 70%. Might be off base, but I'd wager that's the reason