Well, it’s school not daycare.
My youngest daughter is in pre-school from 9:30 AM to 2:30 PM because it’s the only pre-school/daycare I can afford. My oldest daughter’s kindergarten is from 8:15 AM to 3:15 AM and I must may for inn-school care before and after that time.
“Full day” is contextual; it doesn’t refer to my or your full day. As you said, different people work different “full days” and the schools can’t possibly appease everyone. They have to maximize the length of the day with their budget and resources.
You bring up a good point, though; school doesn’t meet our expectations. Not just the schedule, but its quality (American education in general) is inferior compared to many other developed nations.
It’s great that you have some form of free pre-k for your little one and I hope it grows into everything you want it to be.