Cargo bikes are practical if you carry cargo. I'm single, and I live in an apartment. I don't need a bike to haul things home from Home Depot, Costco or Sam's Club. I don't have a need to go to those places. Thus, I have no need for a cargo bike. Pair of grocery panniers and a trunk bag carries all the stuff I need to carry. If it's a good sale that week, I make two trips.
What I'd like to have an excuse for is a trailer.
I'm single, but I tend to do my grocery shopping every two weeks instead of one or two times a week. That makes a cargo bike really useful. Plus, I have a cat, and a pseudo-yard behind my apartment that I want to do a bit of gardening in. Hauling cat food, cat litter,
and groceries, not to mention gardening supplies, is tough with just two panniers and a rack trunk.
That said, I don't think I'd want to use a dedicated cargo bike for commuting.