Because if the potential were seeing in research on fmri neurofeedback for example does work, we might be talking about something that will make virtual reality look insignificant.
One example is accelerating mental learning processes that take experienced meditators decades(they call it enlightenment which leads to development of deeply happy and caring human beings ) into a period of weeks/months of a much less intense effort, so the experience may be available to everyone, not just a rare few.