Families with children who adopt this strategy make up a SMALL percentage of park goers on any given day!
Remember, there are a lot of adults at WDW too, and most of them SLEEP IN!!! We do, at least.
Heck, when my sister and friend and I were at WDW last month, we only made it out of the hotel room before 12:30 on ONE day the whole week, and we felt like that was good! Most of the time, it was more like 1:00pm or 2:00pm when we were heading out to the parks.
We slept in until 9:30-10:00, then went to the gym to work out. Then, we ate breakfast in the room, showered, got ready, etc. Three women take some time to get ready, especially with one bathroom.

1-2pm was our "average" out the door time. Since the parks were open late, and there was usually a nighttime EMH until somewhere around midnight or 1am, this worked out just fine for us! We never even used the resort pool, or went back to the room, except to drop off a purchase, or change clothes, or grab a sweater or something. Since we were at the Contemporary, and on the monorail, this was convenient, otherwise we wouldn't have returned at all...