excellent question. I wish more neighboring dojos either cross-trained and/or shared by guest drop-ins, demos or seminar.
In reality, unfortunately, it's egos that block the dojo doors. There are many levels where something could go wrong which would possibly result in loosing students - real or percieved.
first to mention is 'style-pride' (I think you know where I would go with that if I ellaborated).
then there is 'sensei-envy' or sensei-bias. (x sensei could kick y sensei's ass therefore dojo x is better.)
or, if dojo x really WAS obviously better, what would that do to dojo y's student base?
I think you get the point...ego being the keyword, business being the M.O.
Have you ever tried this ...contact a local dojo and ask them if they are interested in getting the classes together on some saturday afternoon for a joint training session...
There is a good chance the conversation would go something like: "Thank-you appreciate the offer, we aren't interested."
I tried participating in a junior high school "cultural arts" demo. I only had 5 minutes on stage and was going to perform Goju-Seiunchin and talk briefly about Okinawan MA. A local TKD school was also giving a demonstration and didn't seem particulary happy about another MA sharing the stage. The attitude of the TKD instructor put me off but I decided to do it anyway
. She insisted her demo be first - no objections from me. Her demo lasted 15 minutes over the already overbooked schedule, and the program director was pacing the floor...I went over to the director and told her since they were behind schedule I'd do it next time and walked out.
Watching the TKD demo, I knew why the instructor didn't want a contrasting MA performing. her students (and her self-held board breaking) were nothing less than embarrassingly terrible. The higest rank student-a 30 something red-belt couldn't kick higher than groin level without loosing his balance with arms flailing. the kata looked as though they took random people off the street and taught them the kata 30 minutes prior to the demo.
The youngest boy (yellow-belt) was the most impressive with his successful jumping over a body and kicking wood. The other breaks were less than successful with the red-belt bouncing off of 2 x 1/2" pine boards when he attempted an elbow strike to break them...he finally did it on the 3rd try. There was J.H. school student muffled-laughter during the demo. lol actually, it was THE worst demo I've ever seen of any MA.
My point is, if ego, politics and games like this go on even for fun cultural events, imagine the uphill struggle it would be getting to train together!