First of all, welcome to TxBands! We don't get to many kids from South Texas posting on here anymore but we are glad to have you.
Well having competed in the La Joya regional twice, I can definitely say it was a couple different factors.
The BOA entry fees are usually higher than other local contests which led to a lack of interest in this particular regional. There was another regional scheduled for 2006 in Donna but those were some of the reasons it was cancelled.
As for retreat, at our region 15/28 contest, there is a full retreat/pass in review and all the division announcements are read. It is much like the BOA retreat but there is a little bit more pageantry involved.
Hope this helps!