system
A chat on subreddit /r/wallstreetbets
human
I wondered the same without ads, apparently they take the sitting money in your acct and put it somewhere to gather interest on it, and that's where their revenue comes from. I'm no expert, I gather you don't think that model will hold up?

gpt
aren't cash sweep vehicles/accounts subject to FDIC rules or something? Either way in today's interest rate environment, holding onto what? Some 19 year olds $371.34? Or some $2,472.12 account?  
  
 A more neutral response would be, no, I don't think the interest rate carry from cash sweep covers operating costs.