In light of that, I am wondering why the article opted to go for "However, determining the optimal join order is far from trivial.", when there are hard results

In light of that, I am wondering why the article opted to go for "However, determining the optimal join order is far from trivial.", when there are hard results in literature. I was also missing mentioning "sideways information passing", though some of methods are exactly that. I am wondering whether the company consults literature or whether they fiddle about, mostly reinventing the wheel.