(6) Another possibility (related to (2) and (4)) is that academic social scientists are primarily in the business of sharing information with other academics in their field, so they tend to rely on tools that are already standard within their field. A paper that uses complicated statistics which their colleagues don't understand is going to have less impact than a paper that makes the same point using the field's standard tools. It may also have trouble making it through peer review, if the peers don't have the technical knowledge to evaluate it.

So the incentives aren't there for an academic to stay on the cutting edge in adopting new complicated techniques. People who are in the business of building things to get results have a stronger incentive to adopt complicated new methods which offer any technical advantage.