Instacart/deliveroo provide all of those advantages - plus - someone to unload the groceries and bring them to your door, which is definitely better. And a human to talk to if there's an issue.
Consumers don't care one bit that their groceries were delivered 'autonomously'.
The 'advantage' of the 'self driving' in the end must be cost - and frankly a significant reduction in cost - or it won't pan out.
In this scenario, there still has to be a picker, a checkout, a loader, and some human overhead on managing a live fleet of cars. The 'savings' will be on the cost of the driver - and that's it. There's also a deficit in experience related to the fact it might not work well for apartment buildings and can't unload etc..
After all the fuss, ops and overhead, this tech has to take the average grocery+delivery bill down by a fairly quantifiable amount or else it won't make sense to use it.
It will happen eventually, it must may not be this company at this valuation.