I have actually mostly gotten this strategy from very dedicated teachers. It's meant to address a strategy clever and grade-seeking students work out very quickly: without something like this, constantly asking for regrades has zero cost, and occasionally benefit to you.

This moves regrade requests more toward "No, I checked over my exam again and I'm sure this is a mistake..." rather than "Maybe I'll pick up another point or two..."

This was what we taught to say when I was a tutor for a university. The point was the student could not come and just point out that something was wrong with the marking and they deserve more points. If they thought the grade was not fair it could be remarked, but the whole thing would be remarked and a totally new grade assigned. You might come out better or worse for it.