Moralizing Convenience
Before Spotify, it was common for people to convince themselves that they were pirating music to stick it to the labels, who were supposedly treating the artists unfairly — better the artist gets nothing at all then too small a share. Today we can laugh at such rationalizations. Of course, people were pirating music because it was convenient, and once Spotify become more convenient, they switched.
Today it is common for people to convince themselves that they are blocking ads to protect privacy or because money is the root of all evil — if you earn through ads, and not by selling luxury devices.
Of course, ads are way better for privacy then paywalls and even donations — you don't have to give someone your credit card number if they monetize their website with ads. Paywalls as a business model are bad for privacy even before you're asked to pay, because the first step to getting you to pay is getting you to make an account. Ads are the reason so many services exist which do not throw a "sign in" popup in your face. For an ad-funded service, that would risk you closing the tab, which would directly lose them money. For a paywalled service, if you don't want to login, you're a lost case anyway.
Of course, money is the root of all evil — regardless of how you earn it. If you want to monetize a website, you have to get into people's way somehow. They want to do whatever they want to do, and you show them an ad, ask for a donation, or hide whatever feature or content they want behind a paywall (or a loginwall as the first step to get them to pay). All these things can be done in an honest way, and yet the temptation for dark patterns is always there. But what if you're not running a website at all? What if you're selling luxury devices? Is that not a business model that is morally pure?
Well, compare iMessage to WhatsApp. Everyone with every device can use WhatsApp as an equal. iMessage is only accessible on Apple devices.
In the anti-ad worldview every morally questionable action by Google and Facebook is blamed on their ad-based business model. But have these companies done anything as cartoonishly evil as building a social network that excludes people who can't afford an expensive device?
I'm sure the founders of Spotify pirated music themselves, but they did not rationalize and moralize their behaviour, so they were able to think of a better alternative.