Why don’t we tip IT service people?

You tip the pizza man, you don’t tip the Fed Ex driver. You tip the bartender at the pub, and you don’t tip the McDonald’s clerk; but you do tip the barrista at Starbuck’s. The US has ritualistic levels of tip etiquette, which admittedly don’t exist other places in the world but, the question remains; Why don’t we tip our IT service people?