I used to order food a lot when I lived in a college town and always tipped generously and texted a thank you note to the drivers afterwards. I have done delivery jobs in the past as well and know that you often get the same drivers if you order often enough at specific times. They will remember you if you are kind to them and will go out of their way to prioritize your orders and make sure everything is perfect. I suspect many of the people who don’t tip have never worked customer service jobs.