[Ollinson]

Because the drivers are paid a lower wage under the assumption that they will get tips.

If you want to be righteous call the manager at the place you're ordering food from and complain, don't stiff the guy delivering pizza for a living.

[gambiting]

I'm sorry, I didn't realize this was the case where you live. Like I said in my other post - I live in UK, where tipping waiters is completely normal(and no, not because they earn low wages), but an idea to tip a delivery driver has never occurred to me, nor does it make any sense. That's why I asked for an explanation, why does anyone tip delivery drivers. For the sake of avoiding future confusion - what are other professions that are tipped where you live?