Actually, having voted dishwasher (and it's true I have discounted cottages that don't have them), I would expect to have access to a washing machine too. It's more that there usually is a washing machine but isn't always a dishwasher (though usually is now).
The main reason being bed-wetting children. Other child mess also possible. (On which not you must have waterproof mattress protectors on all beds, not just the bunks, as a child who's unwell might crawl in with their parents).
Sometimes there's been a laundry room for a group of cottages, with pay per wash slots, which is fine.
There is clearly an expectation that people don't really cook on holiday (there's never an adequate range of kitchen equipment) but we do. We like cooking, it's much cheaper than eating out and, with small DC especially, would rather cook what and when we like. Washing up is drudge work though.
But, if you're going to have a dishwasher, you need to supply enough crockery to last a day, three meals. The stupidest thing about most holiday cottages is that you get a dishwasher but only enough plates and bowls for one meal, so either you're constantly running the thing a quarter full and having to be really alert to your future need for crockery, or you have to wash up after every meal anyway.