This is true. I can easily burn through all my daily ad spend on Reddit at rates of between $0.50 and $1.00 CPMs. And the click through rates are awful.

On Facebook or Google, you've often got to spend at least $5-$10 per mille to be competitive in most verticals. $25 to $50 in some verticals like insurance. And it converts.

The reddit userbase just isn't as monetizable.