Because at the age of 2, he walks through stores unassisted, walks through the mall, and goes on my daily walks with me, as well as goes outside and plays and does the typical 2-year-old tearing through the house and still has energy to spare. He is an active child and has absolutely no need for a stroller now and will certainly have no need for it then, when he's 4.
Yes, mortified. My stepson is 4.5 years old. He never, ever, ever uses a stroller anywhere outside of Disney. He is highly active and has no problems walking around extensively on a daily basis. He is too old, he is too large, and he's perfectly capable of walking around, especially with frequent breaks. The choice to put him in a stroller at Disney had nothing to do with what he was capable of doing in terms of moving around, but more the laziness factor in that it's easier to shove him in a stroller and walk around then it is to hold his hand and walk or otherwise pay attention to where he is and what he's doing. I'd have been highly embarrassed to have a child who's almost 5 using a stroller.
Some people may or may not have medical needs that justify their 5, 6, 7, 13 year old, whatever, to sit in a stroller. Most don't. I dare say most kids of that age don't either. If somebody wants to put their kid in a stroller who's clearly too old, that's fine and that is their decision, I certainly won't boot them out or tell them that they're too old. But I will certainly think it, probably point it out to my other half, and lament how people rely too much on strollers.