> if they have the ability to detect and block fraud, then why block accounts?
To protect their business by protecting their reputation.
The scale of Google's advertising business(es) means that a loss in revenue from poor public perception of their ads is likely to be far more than a few thousand small ad buyers (those spending <US$5000/mo) getting cut off, which would barely register as a rounding error (<0.1% of just AdWords revenue alone.)
They could be shadow banning them or they could be continuing to allow them to operate in service of their algorithms. The public doesn’t see clickfraud but they also don’t see headlines about Google ads having a fraud problem.
A rare anecdote of Joe Schmo not getting his 97.54 payout is effectively meaningless.
I understand this, but it's suspicious when they manage to detect the fraud only when it's time to pay out the revenue to the site owner. It's also a little unfair to assume every detection of fraud is 100% purposeful action by the site owner and permanently terminating their account without even so much as a warning. In my case, I had ads running on my blog. It took 4 months to rack up $100. I think the chances I was purposefully defrauding them was low, given how long it took to get to the payout point.
To protect their business by protecting their reputation.
The scale of Google's advertising business(es) means that a loss in revenue from poor public perception of their ads is likely to be far more than a few thousand small ad buyers (those spending <US$5000/mo) getting cut off, which would barely register as a rounding error (<0.1% of just AdWords revenue alone.)