Based on anecdotal evidence I fear/suspect that metrics, luxury journals, and funding pressures have led to a shift in how some/many of the best researchers operate.
Thirty of more years ago the best researchers would operate as follows.
They would pick a difficult problem/area, work on it for a few years and when they had (hopefully) solved it they would write a few (1-3) papers about it. They would then find some challenging new problem to work on. Meanwhile lesser researchers would then write papers that would work out more of the details of the first problem.
Now, people want to work on lower risk problems with guaranteed steady "outputs". Thus, they are reluctant to "move on", particularly when they have a competitive edge in a new area. It is easy for them to churn out 10-20 more papers on natural "follow up" studies working out all the details. They are "safe" projects for graduate students. These papers may be valuable but they could probably have been done by lesser talents. From the point of view of advancing science it would have been better if the successful leader had moved onto a newer and more challenging problem. So, why don't they? Because their publication rate might drop significantly and it would be risky/difficult to supervise so many students on new projects.
An earlier post, raised the question, Why do you keep publishing the same paper?
Is this a fair assessment? Is my concern legitimate? Or I am just naively nostalgic?
Aside: I am on vacation. You should not work on vacations. This post (and the next one) was written last week and posted by delay (cool, huh!).