First, people that want to be professors normally do so because they want to steer their research agenda, not repeat what other people are doing without contribution. Second, who works in their lab? Most of the people doing the leg work in a lab are PhD students, and, to graduate, they need to do something novel to write up in their dissertation. Thus, they can’t just replicate three experiments and get a doctorate. Third, you underestimate how specialized lab groups are — both in terms of the incredibly expensive equipment it is equipped with and the expertise within the lab. Even folks in the same subfield (or even in the same research group!) often don’t have much in common when it comes to interests, experience, and practical skills.
For every lab doing new work, you’d basically need a clone of that lab to replicate their work.
