Do gas stations have any incentive to provide skimmer scanning? I'd imagine most of their customers aren't even aware skimmers exist, so adding them probably wouldn't attract many new customers. And the margins they make selling gasoline are already pretty thin, so it's possible that the cost of adding scanners to all their machines is less than the extra money they'd make from the minority of people that would go out of their way to give their business to gas stations with scanners.

If gas stations are liable for losses that customers experience due to skimmers it's possible that gas stations would be interested, but they could just as easily decide that it's worth the risk of having to pay out lawsuits given that I'd imagine it's pretty hard to prove in court that your card was stolen by a skimmer at any one particular gas station considering how many different gas stations any one person uses on a regular basis, not to mention the variety of other vectors that your card could've been compromised through.