The story I've heard is that there's a bit of creative accounting involved -- the driver's compensation from the delivery service is reduced in proportion to their tip.
Ironically, restaurants are by far the largest tip-stealers.
For example, in DC, where minimum wage is $14.00 per hour, wait staff need only be paid a wage of $4.55 per hour on the basis that their tips will make up the difference.
I believe this applies to any job where gratuities are expected to make up a significant fraction of income, hence delivery service drivers also.
That rule is unfortunately in the minimum wage law of every US state that has a minimum wage, as well as in the federal minimum wage law.
Whether you believe this is fair or not (I do not) some restaurants engage in actual tip stealing by letting the managers or owners simply pocket all the tips. This was made illegal in 2012 but that rule was revoked in 2017
