Lots of lenses are on sale, because they are not selling. The story is the same across all brands of cameras and lenses. If you are a business with a lot of inventory but little sales, then you do what it takes to move it.
On the other hand, why would a company spend huge sums of money for lenses that won't sell. There will always be some new lenses, just to meet competition, or company goals which might go beyond worrying about short term profits. Canon seems to be plunging into Cinema in a big way, and you have to pay to play.
Hmmm. Really? Does Canon not offer rebates every year?