In theoretical physics, one of a researcher's main concern is to not to make wrong claims. Granted this risk aversion has its own downsides, but the upside is that he is extremely careful on what he takes to be true. So it's not true that not reproducing the research you rely on has limited benefit. It has the huge benefit that the researcher convinces himself he's not introducing wrong premises. Research is already difficult enough without making mistakes in this silly way.

If your research is mathematical or involves a lot of engineering, you are building on earlier results. In many cases, your own results will depend on the correctness of earlier results in a measurable way. You end up replicating others' research without even trying.

Empirical research is harder. You cite earlier results, but there is no clear connection between their correctness and your results. Especially if effect size is small. Earlier research has more effect on the framework you use to interpret your results than on the results.

Academic researchers rarely replicate others' results, because it's expensive and not particularly interesting. People typically come to the academia because they want to work on something they personally find interesting. If you want to have experienced scientists working on something administrators tell them to do, you better pay industry-level salaries.