Trendy fields often have lots of money in them in both the short term(grants, associateships, funding), and the medium term(first job prospects) as well as benefits like preferential appearance in journals(if two equally insightful articles are up for one spot, would you rather take the article on the topic many are interested in or the article from a much more niche area?) and possibly more low-hanging fruit since there is so much more work to piggyback on/respond to/extend.