I've never run a blues jam, but I have played in the house bands for popular/well attended blues jams quite a bit and have observed the machinations that the jam leader/organizer has to do and it's nowhere near as easy as it looks to make it all work. A few challenges/issues that often come up ...
1) More players attend the jam than there's time for everybody to get a decent shot.
2) Some players don't want to play with certain other players and/or only want to get up with the A listers.
3) The organizer has to assemble coherent ensembles with someone to sing from a disparate group of players.
4) Some players hog the stage by soloing endlessly which leaves less time for the players who follow them.
5) It can be tricky to balance entertainment value/fun for participants when total beginners want to play.
6) Bands or groups of players will want to get up together to perform a showcase of songs they've worked on.
7) Sometimes it seems like every bass player in town shows up and other times hardly any.
8) Some players will show up late and want to get squeezed in.
Bottom line, it can be difficult to make everybody happy.
WOW -
Almost exactly what I have run into SO MANY times!
YOU sir - nailed it!
AND - Sometimes it goes really well too!
Any chance you know Reid Doughten? Curious......