I wonder how much knowledge is lost because the research isn't "popular". What is the opportunity cost of so many researchers doing string theory research, not

I wonder how much knowledge is lost because the research isn't "popular". What is the opportunity cost of so many researchers doing string theory research, not necessarily because they believe they'll find a breakthrough (obviously, this doesn't describe most), but because they won't be able to get published or find a research position if they aren't doing the "in" thing. This doesn't just apply to physics, but the history of physics makes it easy to find case studies in this.