Because they focus on gaining market share at all cost by providing services below cost (eating into their cash reserves), with the hope that once the competition is eliminated, or their market share is substantial enough, or automated driving comes in and eliminates the need to pay drivers, they can recoup their money.
It's a fukked up business model. The same with UberEats and all these fukkers. All fugazi.
The truth of the matter is that if you pay the driver fair compensation for their time and mileage, it's really expensive to order food in. They been subsidizing it for you which is why you haven't noticed. But if the true cost of ordering in was felt a lot of people would simply pick that bytch up themselves or cook.
Ditto for Uber but that's another story