I would think, not many. It really is a somewhat solitary endeavor. I've hooked up with a couple members when I had permission on a larger property and enjoyed it. I generally hunt with my brother, Steve. Hunt's are usually scheduled a day or two ahead of time so not much time to "organize" a get together. Many sites are fairly small, houses, small farms etc. You just can't have too many guys on them. Then you couple the fact that many MD'ers have specific types of hunting they enjoy or pursue. I'm glad for the guys that like to go to a tot-lot and "pop" clad. Frankly, I'd be pulling my hair out doing that. Some guys like curb strips and tear outs, you name it. We hunt almost exclusively colonial, particularly Revolutionary War sites.
Some I'm sure, myself included, have a reluctance to spend months researching a location, going thru the maps, books etc and finally identifying a likely location and procuring permission if needed. As hard as some types of sites are to procure, yea, one is reluctant to bring in basically a stranger and have him pop out that beautiful pewter uniform button. I mean honestly, you've spent years looking for that thing in a sense. Mind you, I have had a few members join me on primo Rev spots, but they were quite large, the sites that is, not the members
. I plan on doing it again, but only when the site warrants it.
I would also suspect that some guys don't think their spots are all that worthwhile and don't want to have others waste the time and effort to spend an unproductive day.