Most certainly, there are some lazy people. However, for some, it can be considered good management of time resources. It's not unusual to have both parents working, or of course, a single parent. In our "cadet orientated world" there are 2 evenings a week parental taxi service, plus any weekend events. Add in after school clubs, extra course work, normal family life, & available time can be restricted! Depending on the age of the kid(s), sometimes it is much less hassle & stress to get the little b*ggers together to drag them around the store. Put them to bed, have a glass of vino, wait for your delivery.
It also depends on the location of your supermarket; I consider us to be well-served with different choices, but from leaving the house, to putting the first item in the trolley is about 30 mins. Say one hr to shop, 30 mins to load car & get home. So, whilst it's only 2 hrs in total (& maybe a gallon of fuel & associated running costs on the car), for some families, that is time better spent at home - & of course, some people work from home too. You could argue that by buying on-line, you also don't get caught by the "you really need this super item" offer!