I haven't read all the posts so apologies if this has already been covered.
Around here, Stagecoach recover the costs of concessionary pass users on an average fare for the route basis. Capping the maximum fare would reduce the average fare paid (if it's based on the actual price paid, rather than that in the fares book) and thereby reduce the concessionary pass income. This could be quite significant.
As an aside, the free pass for the old demonstrates that bus travel is not price-sensitive; even at the lowest price possible, free, there are many concessionary pass holders who never use buses.