I don't see those obvious reasons.

The way airlines distribute miles, they seem to have nothing against people accumulating them. Anyway they retain total control over what you get for them. So unlike mistake fares, where they really lose money, MR's shouldn't ring any alarm bells at airlines.

This leaves the possibility that someone who has figured out how to do MR's wouldn't want to reveal his techniques. Fair enough, but in this case that can't be as he is giving free seminars again and again.

So I don't know what the obvious reasons would be.