> it makes sense because ads subsidize those phones.

It's not about the cost of the phone. If it were they'd stop pushing ads the moment they'd earned back the full cost of the discounted phone you bought. It's purely about greed. Companies push ads so they can stuff more cash in their pockets over and over again for years, if not decades, after the money they got from your initial purchase. It doesn't matter if the phone was $100 or $2000 because ads increase their profits in either case, and money is literally the only thing they care about.