But many restaurants don't make any profit after the 25% cut. Pre-covid you could write it off as a marketing expense but when in-person dining disappears you're faced with option to close or keep open and make a loss or no money on every DD you get.
This is partly why 110,000 restaurants have closed since the pandemic
Like you said here, with DD around it does give some restaurants a lifeline they wouldn't otherwise have. Plus the government gets more tax revenue, over time some large percentage of the currently $60B valuation created by Doordash, which could be used to help the rest of those hit hardest by the pandemic if our democracy wasn't being held hostage by one Mitch McConnell.
I feel that regardless of your feelings on the truth of that last quote, the connection can still (and will) be made by many people.
To be fair though, not all tech is similar. I don't think people mind Amzn charging the seller 5-15% and paying the delivery guys whatever it takes. I hope food delivery apps become more reasonably priced- or then maybe Amzn comes after their margin!
I don't order delivery anymore, for $20 I'll pick it up myself.
From my back of the envelope calculations, it seems that the conditions necessary for a restaurant to break even or make a tiny profit with delivery apps that take a 30% cut exist but are narrow. For the restaurant to cover that fee, it would have to increase its online prices by 1/(1-0.7) - 1 = 43%, which would make it less competitive to a segment of its consumer base.
On the other hand, if the app's fee was 15% (which it is in Chicago, due to a city-wide cap), a restaurant only has to increase its prices 1/(1-0.15) - 1 = 18%, which is more palatable and less noticeable.
It does also create cash flow, and there are various things you can do with cash flow.
If you can increase sales velocity, the increased returns might be able to help profitability (though the counterfactual is hard to prove -- if you didn't have the apps, would velocity have been lower? Hard to measure).