I know for us it isn't really about the waiting. It's about the wasting.
There are just so many better things we feel we could be doing with that time. A day only has so many hours. I'd much rather plan out and ride 3 rides in the same time someone else going with the flow might ride 1. There is just so much to see and do. We aren't local and don't go all the time. When we do go, I want to make sure we can fit in everyone's favorites.
Also, if the whole family goes, we have a large group of people. If everyone only picks out 1 or 2 things they want to do each day, there is no way to fit that all in without maximizing our planning and minimizing our waiting. Which person do I tell, sorry we ran out of time to do your choice? It just doesn't make sense to us to waste time waiting if we don't have to.
Our plan is usually rush around, minimize waiting, see as much as possible in as short a time as possible. Then after we've hit all the attractions on our to do list, we can go with the flow the rest of day, (exploring, shopping, parades, shows, scavenger hunts, whatever) and really enjoy it knowing we aren't going to run out of time. If we tried to go with the flow from the begging, we'd be a nervous wreck, worrying about running out of time.
Which brings me to my next point, going with the flow isn't relaxing to everyone. I learned the hard way going with the flow does not work well for our family. It isn't relaxing to us, but instead is stressful. We don't enjoy not knowing what we are doing next, and we really like knowing we have a set detailed plan that will allow us to fit everything important to us in. As silly as this sounds, it is comforting and helps us relax and enjoy the trip. The first time I tried going to a park and going with the flow, no plan, it was a complete disaster, definitely not relaxing in the least.