Why is a scammer not considered automatically eligible for a refund?

I was contacted tonight by a scammer. I've gotten this same scam 3 or 4 times now, it's always the same story. Had i gone along with the scammer, I would have lost thousands of dollars to their scam.

I contacted thumbtack for a refund for that lead. And I did get a refund. But the email i received said it was a courtesy refund because this lead is not normally eligible for a refund.

Again, to be clear, I WAS issued a refund. But to quote the email I received: "Although the charge for the lead, <deleted>, is not eligible for a refund under our policy, we gave you a courtesy credit. We don’t usually grant courtesy credits..."

How is a scam lead not considered worth a refund under your policies?