Washer / dryer combos do exist for tiny home RVs, which are about the same size as an under-counter refrigerator. They can be put in our models and we have installed them for customers.
Please see the attached Buying Guide.
A conventional size washer / dryer takes up significant amount of space is normally not installed in a tiny house.
Tumbleweed offers washer/dryer combo units as a standard option in our Tiny House RVs.