It can be a hard problem to solve, but it is frustrating. Google ads has a threshold billing system in place (based on their public docs). What this means is they probably track how much each payment method has spent, and charge that payment method when it reaches $X.
My theory is below, but I have not researched or looked into virtual cards.
The problem with virtual cards or privacy cards: What's stopping a single physical card from having multiple virtual cards generated for it? So if someone had a card they knew could only be charged $100 and googles threshold is at $200, they could make 10 virtual cards and add the physical card resulting in 11 payment methods. Now they can theoretically get $2200 worth of ads (if all ad campaigns reached the threshold at the same moment).
In other words, fraud risk can go up significantly.
My theory is below, but I have not researched or looked into virtual cards.
The problem with virtual cards or privacy cards: What's stopping a single physical card from having multiple virtual cards generated for it? So if someone had a card they knew could only be charged $100 and googles threshold is at $200, they could make 10 virtual cards and add the physical card resulting in 11 payment methods. Now they can theoretically get $2200 worth of ads (if all ad campaigns reached the threshold at the same moment).
In other words, fraud risk can go up significantly.