I think people who lose weight at WDW generally do not exercise as much as you in daily life. I run about the same amount as you and I don't feel like I get the same exercise at WDW from walking.
I don't like to spend time running at WDW either. Last time I tried make excuses for extra walking. For example, I would volunteer to get the fast passes for everyone and speed walk to the destination. This was the first time I didn't gain at WDW and I think it was because I did the extra speed walking when I could. I did eat the Kitchen Sink