Reddit isn't providing free content, the users (or whoever the users got the content from) are the ones providing the content. None of them are paid. Reddit is only a host and would ideally be replaced by a public utility or community-run alternative.

People miss the forest from the trees when it comes to social media claiming the users make the community. While it is completely true, it's not the complete picture. The communities have to be fostered. I'd be willing to make a bet that any alternative websites and/or communities will not rise up to replace Reddit because it's hard to foster a social network. Way harder than the individual parts of moderation per subreddit. The people who think otherwise are most likely living in a fantasy Utopia