Story: Sanders under fire from Senate Democrats
This human failing has a name: Status quo bias. It is just one of quite a few biases that stop us from being rational and move away from what we're doing, even when it would be overwhelmingly positive to make changes.
I think this fear is also tied to a tendency we have to keep connected to the past in some fashion. We find meaning and support from linking where we are today with what we think happened in the past. We do this with religious texts, people & families, constitutions & laws, social traditions, etc. This impulse also leads us astray by giving too much weight to expired circumstances. What we did before were decisions not only misinformed by our many biases, but falsely point to what we should do now because we're not taking into account that conditions have changed, as they always do.
In order to improve how we and our descendants live, we must embrace rational changes based on the best information we have about our current conditions and minimize as much as possible the power of our biases to give us comforting false answers.