Well, yeah, but without students & postdocs it is very difficult to make a material impact on your field of endeavor.

There’s also an ulterior motive for some lines of work, where sending a paper to be critically reviewed by rivals is a mechanism to torture test the work & conclusions.

This can be taken too far (especially in biology, the glam fluffing and $million additional irrelevant experiments are legendary), but in principle, if even your most motivated critics can’t find a fatal flaw in your work, it’s a reasonable bet that the work is sound. At least, that’s the principle. Editorial overrides sometimes break this safeguard, though (lord knows I’ve seen a few).