Here is a really interesting one.
Originally, religious fundamentalism included values such as fighting poverty, creating world peace, ending hunger as well as outlawing abortion and gay marriage.
But those first few are very difficult to do, can't be done 100% or permanently.
On the other hand, outlawing abortion and gay marriage are binary laws or Supreme Court decisions. They are easier to accomplish and certainly easier to talk about in sound bites.
So abortion and gay marriage got more repetitions in ads and speeches. They therefore became stronger connections in the schema of both the population listening and the fundamentalists and politicians speaking. So eventually, these issues dominated the agenda at the virtual exclusion of the rest.
So the human factors of the process drove the setting of the fundamentalist agenda.