The restaurants don't lose a full 30% on the order - the items on Uber eats are marked up over what you pay when you do regular takeout. I wouldn't go so far as to say they don't lose any money at all but we won't know exact numbers until Uber / restaurant owners publish them somewhere.

Also, having a delivery option I'm pretty sure provides additional business (on top of just having dine-in / pick up). So, for a restaurant to hire employees and building out a delivery service themselves will be much more hassle and probably will be more expensive than using a service like doordash / uber eats.

Lastly, this is driving a trend towards the so-called "cloud kitchens" letting restaurants operate with a subset of staff in cheaper to rent places and charging effectively what a regular restaurant would for a meal.

The restaurants are going through a paradigm shift now, and it will only be accelerated due to COVID - Cloud kitchens can be more sanitary / safer to order from than regular dine-in restaurants for instance but I don't really feel sorry for them. If anything, the drivers doing the delivery are the ones getting shafted here and barely making any money. If folks start tipping, it will simply mean that Uber can afford to pay drivers less - the amount a driver makes won't change very significantly.

Overall I'm convinced eats is the future and Uber focusing on ride share + eats + self driving (existential threat if someone else does it cheaper / better) is the right way to go for the company.