Obviously, in that scheme Spotify would have to charge per streamed song too, and that would cause monthly payments to drop straight into the toilet. Neither Spotify or the record companies are that stupid.
Spotify's incentive is to keep people subscribed, and keep the record companies on board. For a decade, they were actually the best at fighting spam/fraud by a mile. (Then they fired the guy who did most of the spam-fighting for them. Worth noting here that the record companies actually own a huge chunk of Spotify).
For keeping people subscribed, Spotify's incentives are actually quite aligned with rights owners: they want the subscription model which collects most revenue. If a $1000 monthly subscription would make them more money, they would do that. If a $1 subscription would make them more money, they would do that (and indeed, that's closer to what the subscription costs in some parts of the world). If a pay-per listen model would bring in more revenue (lol) they'd do that too.
But for keeping record companies aboard, Spotify has a huge problem. Because no matter what Spotify does, the rights owners incentives are to cry bloody murder and fling shit, all the while pulling shit like this (you notice the beneficiary is a superstar who's also an industry bigwig? Somehow, he's not the one getting sued, funny that).