To shed a little light on it, after some calculations it could be that the 2005 Arizona Regional has teams traveling an average of 419 miles, or 7 hours, to visit the regional.
After a bit of further research, if you look at it from a
Porter's Five Forces perspective (a tool used to define competition within an industry so that it can be tackled easier), you're running into the huge issues of "Power of the Buyer" and "Threat of Substitutes".
Power of the Buyer:
There's practically zero switching costs for teams to decide on their regionals to attend, thus the team really has the power over the regional in this aspect. There may be some indirect costs that include missing out on the savings at one regional in the areas of hotel, food, and other stuff, but this is really minimal, especially with THS running their own negotiations for teams on hotels, which is a huge percentage of costs for teams.
Threat of Substitutes:
Arizona is flanked in the timeline by Sacramento and Portland, of which there are 6 teams skipping the Arizona weekend and going to both Sacramento and Portland. Because of this, teams that may normally go to AZ have some other reason to go to both regionals, or they may have good reason to go to one of the two, and skipping a weekend and going to the other makes sense on the team level.
Suggestions:
My main suggestion is a change in marketing. It's obvious that all the planning committees care about putting on a good regional, and thus they're going to all try their hardest to have a great volunteer crew and an awesome team social. The key here is differentiation. Find someone to put in a little extra money (especially a company that thrives on targeting the 14-18 market, such as colleges...a good team social means a captive audience) and do something for the team social that none of the other regionals are offering.
Compared to the rest of the regionals, AZ sits on the higher end of average mileage traveled by teams, so much so that it can fall into the category of "vacation regionals". Capitalize on that vacation aspect by including incentives for teams to travel long distances by giving discounts to local hot spots, restaurants, or flight deals.
I would also suggest to forget about those teams that are close that are traveling to both Sacramento & Portland, but instead build up on the aspect that you have a similar scheduling connection going on between yourself and San Jose, of which there is an overlap of only 2 teams. It benefits both regionals by getting teams to buy into coming to both, so try to work out a deal between both committees to offer discounts that only kick in when a team decides to attend both.
I'm sure you guys will work it out. Good luck!