Loose tenons are just a different way of doing it. I'm not sure why he
does it that way so often, but in situations were you have ALOT of them
to do, the router method can make quick work of it. I use a simple
homemade jig for my loose tenon mortises. You don't need a
multirouter. But when I only have a couple to do, I usually do
integral tenons on the bandsaw.