Why don't more professors utilize their students as research help? With more and more data science students being interested in collaborative communities like Kaggle, and with faculty constantly being asked to do more with the same amount of resources, there seems to my naive mind an opportunity for a more symbiotic relationship.  These community's successes are evidence that many students (in the broad sense of the word, at least) are seeking additional opportunities to reinforce their education through applied learning.  Beyond the obvious ethical issues that might arise from a sort of indentured service, I am curious why more professors don't offer opportunities for students to practice and realize the practical application of their skills by doing even some of the exploratory or data clean up grunt work that most research requires, as this might provide them more time to engage in higher value add activities.
I do employ students to participate in my research. In my department these students (Bachelor and Master students) are paid. That is the first limit to the number of students I can employ: I can only employ so many students as my budget allows. 

The second limit is that in the kind of research I do these students cost me more time than they save (unless they are really good). Doing real research is for them a whole new experience, and they have to learn. That costs time, I need to do a lot of explaining, errors happen that need to be found and than fixed, etc. 

That is fine, giving them that experience is why I employ them. They can see if this is something they are interested in pursuing as a long term career. If so, then they start with a bit of experience. If not, they are saved from starting a PhD and than dropping out. Either way is a positive outcome for them. For me, employing students for research is more a teaching task; an enjoyable and rewarding teaching task, but not something that I expect to improve my productivity as a researcher (If it happens than that is a nice bonus). 

This obviously depends on the kind of research one does, and the kind of tasks that needs to be performed to do that research.