Small children don’t understand the concept of time really. There’s either now or not now. When I wake E up in the morning, he tells me he was napping. Waiting for a play date an hour away might as well be days (so I often don’t tell him until it’s almost time). And they certainly don’t understand what it means to be late somewhere.
All that to say, grown-ups like to rush small children, and small children don’t understand why.