A cynical guess is that in politics you only fight for rights of people when it is profitable—if you expect that in turn they become your voters. You care about minorities either if they are large enough, or if other groups feel like they are in the same reference class.
Apparently, psychiatric patients are not numerous enough (to vote for you in return for your help), and other groups of people do not identify with them enough (to vote for you in return for your help to them).
A cynical guess is that in politics you only fight for rights of people when it is profitable—if you expect that in turn they become your voters. You care about minorities either if they are large enough, or if other groups feel like they are in the same reference class.
Apparently, psychiatric patients are not numerous enough (to vote for you in return for your help), and other groups of people do not identify with them enough (to vote for you in return for your help to them).
Other possibilities that spring to mind are:
The difficulty of them becoming your voters
The opportunity has been overlooked. (The market is not all knowing.)
It conflicts with other interests already secured.