[fuzzybeard]

The cost difference between a moderately sized washing machine and one that's a few cubic feet larger isn't that much. Over the lifetime of the machine it pays off.

And if you have the extra capacity, you'll use it more often than you would if you had to go to the laundromat for the annual duvet cleaning.

[jessaustin]

In many places, water is scarce enough to discourage industrial-sized washing machines.

[api_or_ipa]

Unfortunately initial cost isn't the only constraint. Apartment style top/bottom washer/dryer combos can only get so big. In addition, larger equipment requires greater amounts of electricity to run and maintenance can be a bit more expensive (larger parts).