I wonder if it is actually the pollsters. It's my bet that politicians these days are almost entirely guided by what are seen as majority influences. However, sometimes what they public says it wants, and what it really wants are two different things.
People need to be motivated to action. Sometimes that takes a leader that will take a risk or "go out on a limb". Right now what we have are two people trying their best to be careful and tow the center line while reaching out ever so much to their base. If we had 10 candidates on a ballot, all equally funded. It would not come down to who towed the line but who inspired people with big ideas. Unfortunately, Obama did this but hasn't delivered on what I think his biggest promise was, which was to transform politics and be more transparent. Granted transforming politics is a tall order, but being transparent within your own administration is well within his ability. I digress though.