The software isn't really the hard thing about these companies, the customer and provider UIs are nothing special and they achieve their scale using fairly industry standard event driven tools and cloud compute. They all talk a lot at industry conferences, so it's no secret really.

Ensuring a restaurant will make the food for an order, ensuring a delivery person shows up to collect it, ensuring that food makes it to its destination in the same condition it left the restaurant, ensuring everyone gets paid at the end.

Preventing any of that from going wrong and handling it when it does is where the value of these companies lies.

Who is going to step in if a restaurant starts ignoring orders, or a driver starts eating the food, or a customer does a fraudulent chargeback?

Then there's the money issue: where does the money go when people pay? Who owns the merchant bank account? Does every driver need a merchant bank account? How is tax accounting handled?

You can't use cash for this system as both the driver and restaurant need to be paid (and TBF, whoever is paying for hosting the back end servers), and the driver won't necessarily go back to that restaurant