It's not about low-income people. Those needs are actually quite common among upper-middle class American vacation travelers with children so I assume you don't know many of them. Regardless of expense it's a huge hassle to drag multiple small children to a restaurant for three meals per day for a week. For at least some meals it ends up just being a lot easier to heat up something in the hotel room.

I am well aware that hotels will provide cots. Cots are torture. No one wants to sleep on a hotel cot. And even if hotels have adjoining rooms they often won't guarantee to give them to you when you make a reservation. It makes no sense at all.