2x drop not entirely increasing drop rate for area bosses?

I've been playing from beta til now, and needless to say, I hunted MM quite a bit. Yet when I decided to stop by for fun, an Ilbi pops out. First and only ilbi from MM in 5 years worth of hunting.

Also, there're days when I get nothing off wolf spiders whereas there're other days where I just pop in and an ilbi drops.

Moral of the story: having an increased drop rate does not guarantee anything other than possility.