If this is true why do so many GMs spend so many assets every year at the TDL?
Are you saying that all these GMs are wrong?
Wanna know the reason why they do it? They are rewarded for it.
They're commended for overspending for short-term fixes before the playoffs, because there is this consensus that the playoffs determine who the best team is. It is objectively the wrong take, as playoffs have been proven to be mostly about luck, but find me a fan who prefers the President's over the Stanley Cup. Won't be that easy. On the other hand, if your team loses a couple of coin flips in the playoffs, especially in consecutive years, that can be the end of a GM. Therefore, in come the rental trades. A single player added to a hockey team makes next to no difference in statistical terms, but fans demand that they add their shiny toys.
And yes, there are so many GMs who don't deserve their jobs. They consistently do dumb stuff and could probably be replaced by some of the posters here, at least in some respects.