Why are Las Vegas cabbies so weird about tips?

[Nate tha\\\' Great]

Had this experience two times this weekend. The cab fare was like $6.60 or $6.80 and I handed the cabbie a $10 and asked for two dollars back; both times I got a little speech from the cabbie about how hard he worked for his money and wound up parting with an extra dollar. It wasn't like I was representing myself as a high-roller; there were no discussions about my wins/losses in the poker room or anything like that and I was dressed/acting just like some normal low-key schlub. What gives?