> But what I'm struggling to understand is where is the money coming from to run those bots?

I agree, I have a hard time understanding the motivation for this behavior. It's obviously happening, I just don't know how someone benefits from a bot pretending to browse the internet.

Isn't the idea that you run google ads on your site, and then have your botnet click the ads on your site, and you get paid for the traffic?

Aha! that makes much more sense. Yeah having something autobot your click throughs seems like a motivation to run bots.

I was thinking about ad traffic from one of the meta/twitter/tiktok products and couldn't think what the motivation would be

It would but the fact it goes out and does it to other sites is weird. Why would someone else fraudulently click my ads? As an attack, I understand that, I've had that done to me. Just randomly seems odd. Maybe I'm just not creative enough to think of bad things to do with this. :D

Scrape data and package+sell it, either on demand or pre scraped.

for ad networks and social media platforms that provide monetization the click fraud is direct.

there is also a massive industry of fake accounts and fake engagement for social media and SEO (google). bots are designed to create plausibly real engagement, which is used to trick ranking algorithms into boosting content. these bots have to be real enough to bypass platform detection. clicking through on ads is a way of incentivizing platforms not to shut them down and possibly improving the ranking results, working with the theory that platforms give stronger weight to engagement signals from clients that generate more revenue.