Why does anyone become a "guru" in the first place?

[James Reyes]

One thing that has always made me generally distrustful of gurus is the question of what motivates anyone to become a guru in the first place. If the methods and techniques taught are are so great, why waste time teaching? Why not just spend the time doing more deals?

Now, it's obvious that selling courses and mentorships at thousands and thousands a pop is very lucrative. At these rates, it's clear that a guru's motivation is not some altruistic pie-in-the-sky desire to pass on wisdom (not to disparage the pursuit of profits, after all this is why we are all here). There is just this seemingly BS-y aspect to guruism in general. Why not sell a course on how to become a guru?