There are a lot of factors, but I like to narrow it down to be a basic concept of fear. Much of the voting population is older and one fundamental feature of people as they age is fear of change. You’ve lived your entire life under certain circumstances and voting to change them drastically feels too scary for most middle-aged and older people.
Fear is the factor behind every policy and value that people use to vote conservative. Meanwhile, the demographic that isn’t so set in their ways and welcomes change is the young people and as we see with Bernie they don’t actually show up to vote. Just the term “progressive” is rooted in progress or change, “conservative” is rooted in the conservation of past beliefs.