Google also has an interest in preventing fraudulent ads. While the Internet is never going to be "safe", Google does want to avoid having customers actively avoid clicking on ads out of fear.
So they've got a (haphazard, ham-fisted, obscure) mechanism for removing stuff they consider undesirable. It costs them money, but they hope the balance is positive by keeping their reputation up.
That mechanism has both false positives and false negatives (as well as being flagrantly subjective), because it's far, far, far too much for them to examine each case closely. It may be your lifeline, but to them it's just another $10e2 in a $10e11 revenue stream.
