Learning styles vary from person to person, and so does the learning environment. Most of us begin life with group lessons of some kind, whether they're in primary school or extra curricular activities. There are many reasons why this structure is the norm, including economic viability of teaching. I'm not sure that its as smooth a process to unify private teachers to be a part of a larger program, which ultimately offers a broader range of education, as well as the reputation of a prestigious entity.
Included in these reasons for group lessons is the social element. Students can feel like they belong to a team, and they can share questions to help each other learn faster. This is the best case scenario for group lessons, assuming the curriculum is robust, and the educator is adept. Unfortunately, this group learning structure can often work against the interest of some students. For students interested in hands-on subjects that require self-analysis as well as flow, group learning may not be the appropriate avenue.
In this instance, group learning may hinder a student's ability to make sense of their intuitive awareness of the task. While it may be necessary to wonder how other students approach a task that you've also been assigned, there are some cases where wondering how someone else would approach the same process could be detrimental to a student's individualized learning process. Other students don't know the answers you may need to thrive, but a private teacher will have spent enough time to understand how you approach learning.