The more users you have, the more expensive it is to run.
Like, compute, storage, bandwidth, none of that is free. If you’re providing a free service, like Wikipedia, and you have many millions of users, like Wikipedia, your expenses will be enormous. You can either accept donations, like Wikipedia, require payment, or sell your users.
If there’s something you like that’s free online, support them. If they don’t accept donations, well, I hate to tell you, you’re the product.