The app is free and it has no in-app purchase - how do they make money to support development? What happened to "if you're not paying, you're the product"? To

The app is free and it has no in-app purchase - how do they make money to support development? What happened to "if you're not paying, you're the product"? To register, you need to enter your phone number. Even telegram now allows creating an account without a phone number, why is this still a requirement? Thanks, but no thanks. [downvote all you want, but we're complaining about facebook and others, while replacing them with a new, shiny social network, that has the same pitfalls, just because Gruber recommends it - we never learn]