A ton of them do exist but run by grownups. For example, I worked for a web development company which had Petco as a client. The pets.com people were trying to get purchased and they asked us to talk with them. It was obvious that they were running way too much overhead - we’d talk with their technical team on the phone & people would outright volunteer that they didn’t have much to do and were mostly waiting for the IPO lotto tickets - so they failed but today just about everyone buys pet supplies online.

The idea was fine but they didn’t understand they were in a low-margin industry. That pattern showed up a lot, especially where things like shipping were key chokepoints. Cement.com memorably failed but you can easily order building supplies in many places because the real value is proximity and there wasn’t a high-margin business as a middleman.

You are right that DoorDash might be closer to Kosmo (and may also go under). I meant that Amazon Prime showed that a scaled up, same day delivery service could be viable and profitable