Maybe this is natural as consumers are getting used to on demand delivery so companies need to focus on something and be known for it. But, eventually I'd expect to just have one app where I could get anything delivered without having to use app A for groceries and app B for restaurants and...
Same day delivery of a locally available product is rather different. Typically, it has been tied it to the provider of a service directly – such as FTD delivering flowers, or Pizza Hut delivering pizza. Of course this is most useful for products from companies that don't have their own local delivery service. For a third party deliverer in this local situation, warehousing and that sort of logistics is not necessary. Procurement is very different as well. How do you picture the customer ordering something? An open ended delivery service that you tell them to go anywhere in the city and bring you anything you want? That seems like a different type of business, and a somewhat risky one as well, which already exists as various courier services.
I think specialization is more likely. The value from the services is that they have a some sort of menu on an app or website that provides a consistent, curated selection of whatever product, and trusted vendors that not only do you trust, but they trust.
Anyway, the legal situation in the cannabis market illustrates the need for this specialized service to exist.
In some places you can get alcohol delivered, and others, you cannot. I'm sure that as time goes on, and with federal legalization, restrictions will ease on shipping cannabis.
One thing to note is that the black market uses mail to transport cannabis in a major way… Not just the darknet vendors, but many other people. They even make rap songs about it. Home delivery of cannabis has long been popular in dense urban markets such as New York City and San Francisco, also.