People were accustomed to just having a dumb phone and using a desktop computer for things before - no one needs a smartphone! Of course that totally changed.
I order all my groceries online and have them delivered on a regular basis and yes I build up a list but there are always (always! every-week always) things that are needed ad hoc, and other things that wont last between weekly shops (e.g. fresh fruit often wont last a week so you have strawberries for a couple of days then none the rest of the week)
So classic example of where this on-demand delivery is useful could be you've planned a big meal and forgot one key ingredient, or that key ingredient has gone off, or (as often happens) the online grocery delivery didn't have that ingredient on the day of delivery then what do you do? Just not eat that day? Throw out the rest of the fresh ingredients you were going to use to cook that meal that you now cannot cook? Perhaps try another recipe only then to realise that you are missing other things you need for that other thing you are going to cook? Or what if you just forgot to order something you need? Or you have surprise guests and no coffee left? Or unexpectedly ran out of something - e.g. ran out of baby nappies/diapers because the poor kid got diarrhoea and is using them up at 4x the speed of usual .... these aren't the sort of things you can just wait a few days for the next big shop for!
For me right now I just drive 10 mins to the nearest supermarket and pick up any bits (and if I am going there are almost always other things I can get at the same time while there - e.g. more fresh fruit or whatever), but I would certainly use one of these services more in the future if they continue to exist. I personally can wait a few days for new avocados to arrive if mine have gone bad before I've eaten them (the Avocado Lottery is always cruel), but some stuff simple cannot wait (e.g. nappies, baby food, personal hygiene stuff etc)
I do agree though that for the frivolous/impulse use is kinda silly - e.g. you decide you just want an ice cream or a can of coke or something.