Well... that's part of the premise of freemium. They could probably kill ads entirely and like without that revenue, but then why would people subscribe?

For spotify this is tolerable. Network effects exist, but they aren't everything. For telegram, network effects are the whole thing.

"Freemium" doesn't usually work the way people think it does. "Just let me pay to remove ads" is rarely good business advice. If your business model is ads, you stick with ads. If your business model is subs, you might have an ad-supported version for other reasons.

Even in old media, paid channels/papers/etc. still have ads. They don't make an ad free version.