For convenience mostly, especially for working people.

If u use house washing machine, you have to dry your clothes outside (10-15minutes). If suddenly rain all your clothes gg because you will be at work. Then need to redo wash and dry.

If you go coin dobi, 1 hour settle all include wash and dry. Can wear immediately. No need risk rainy days. Furthermore the commercial washing machine bigger, can wash your curtains, bedsheets, blankets etc. These big items some people no place to hang, or their hanging lines are too fragile to support the weights of big items.