[bombcar]

> Why can't they sell ads?

I suspect the real answer is "because ads on Reddit are less than worthless" - so you get ads trying to sell you ways to poo.

I suspect Google is in a position of power so it is to their interest to make it hard to use their ad interface (or no reason to make it easier) because they don't want you to really work out exactly how useless the ads may be.

> What drives ad spend?

Momentum, likely, but I'm not in the business so I can't really talk to the values.