If this is the case, why don't academics also conduct research in groups? There are already research groups, but in all the cases I've seen, each individual member of the research group works on a separate research question. If the current question is "reproduce the results of this paper", usually one individual member works through the paper alone (i.e. conducts research alone) and reports the results to the others.
It seems likely to me that the benefits of studying in groups should also happen when conducting research in groups. With someone else that's intimately familiar with what you're doing, you can understand papers better, catch coding bugs quicker, and so on. The sum is greater than the parts, and one can achieve more in less time. Nonetheless, I don't think I've ever seen a single PhD project with two assigned PhD students.
What is the rationale for not conducting research in groups?
Edit: I'm referring to the kind of group work that undergraduates might do when working together: one is next to each other when working, and frequently bounces questions off each other. Computer programs are written together such that both partners know exactly what each line is doing, experiments are conducted with two pairs of hands (or more), and so on.
My experience is that at research level, this doesn't happen. Computer programs can be written by many people, but usually each person is responsible for an individual section. Others know what the program is doing on a high level, but are not familiar with the nitty-gritty of other parts of the code such as what each line is doing. Expressions of the "I see what the code is doing, but I would not have written it like that" are common. Similarly, the dirty work of experiments (e.g. aligning mirrors in an optics experiment) is carried out by one person. Others might know what the experiment is trying to do, but don't get personally involved unless the main experimenter gets stuck (or if there is some kind of spectacular discovery).