When one has no money, one is forced to use "free" sites. But I agree it's lousy creating the content while someone else makes all the money. Especially if they're advertising things you do not endorse or approve of at all. I'm all for people keeping the lights on, as it were, but the content creators need to be able to do that, too.
But even worse is when they're not only making money off of other people's work, but then they forbid the person even to advertise/link to their own products being sold, even if the products are relevant (eg., an author trying to advertise their own writing on a site for writers, even if they are active on that site and not just signing up to spam it). So you can be a writer who is perhaps just starting out, but maybe published a novel in e-book format, or have an account somewhere where you sell your content some other way... but the site you are building a fan base on won't let you advertise your own book or works so people who have come to like the work you show them on that site, can support you. Because that would be "advertising," or "spam." So all you can do, ultimately, is give your work away for free, for the site owner's benefit.
How nice is that?