Probably the same reasons that teenagers and young folks can't stay home on a Friday night. They've got to be going. Then by 40 we're content to sit home and relax. That's how I see it anyway.
In my experience, the big boys aren't going to crowd around the feeders like the youngsters do. The rut and cooler weather will get them up on their feet and moving. The fact that there are bucks showing is a good sign in my opinion.
That's a real good way to put that!
Mature deer think a lot like cranky old farts(like me!). I'm a whole lot less likely to put everything on the line a piece of tail. I enjoy the confines of my den more than I used to, and I'm a lot less likely to go out in the heat.