No decision was ever made to not supply the centre of Cirencester I am sure, but rather historical circumstances have gone against some premises.
Most Circencester areas that had a pre-existing cabinet were part of the commercial roll-out for FTTC, then another five via the FasterShire project.
But the EO lines in the historic core have missed out plus another 9 cabinets at a quick count.
A lot of the reason will be that the FasterShire project was seen by many as being a mainly rural project, so efforts were made to try and target the value for money areas that also mildly ticked a 'rural' issue.
Or put another way, once commercial roll-out went into pause as gap funded roll-outs took precendent then drivers such as value for money and speed of delivery were key drivers, so a cabinet service 200 premises in a rural village would beat one in a town serving 125 premises.
As for protesting and appealing you can try, you do have elected officials, but outcome will just be some platitudes.
If the people on the cabinet are serious and VDSL2 ticks all their boxes then http://www.communityfibre.bt.com/
allows you to skip waiting for council or commercial roll-outs and gap-fund the cabinet yourselves. If VDSL2 is not going to cut it and money available then gold plating and gap funding native FTTP is a possibility.
Gap funding for a VDSL2 cabinet varies wildly, and they may be a reason such as power to cabinet was going to be billed at £25,000 by the power company so not economic as a reason why you never got done. In fairly straight forward gap funding scenarios raising £20,000 to £30,000 seems to be the order of the day, but until you get a survey from Openreach you won't know.