Two themes influence this:

1. There has always been a tension in representative government between politicians needing to represent/reflect the collective viewpoint of their constituency and needing to act on their more informed opinion so as to generate a better outcome for their constituency (whether or not the constituency agrees at the time). All pols in representative democracies -- and all of our states are such -- are always trying to balance both.

2. Systemic factors -- cost of re-election, personal pride, the sub-culture of the political set itself, etc. -- often function as additional sources of "input" into political decisions, even though some of these factors do not connect to the constituency at all.

If anything, it is surprising that they remain as connected and "representative" as they do.