Who at middleweight hasn't he fought and why hasn't he? I could understand what you are saying Mr D if Golovkin was in a division with 1 or 2 fighters on his level and he hadn't fought them but the truth is there is nobody at 160 near his level. As for Golovkin coming down to 155, Canelo walked in to Golovkins weight class, Golovkin didn't move in to Canelo's. Also there is a small matter that it's the WBC MIDDLEWEIGHT title, that is a title with a 160 weight limit. Canelo isn't so big he decides new weight classes, if Canelo doesn't want to fight at 160 then he can move back a single lb and fight at 154. Golovkin is the best middleweight on the planet, it reminds me of Wladimirs reign at heavyweight, he was unfairly hammered because the opposition was not on his level. I do understand Golovkin can move up and Wladimir couldn't move out of his weight class but if you are 34 years old and still making 160 comfortably then you are a middleweight. I don't understand why fighters can't dominate a weight class without almost being ridiculed for not moving out of it. Have a little look at Carlos Monzon, a HOF'er and genuine all time great in my opinion was a career middleweight, he didn't climb a weight class, he wasn't expected to, he just dominated his weight class for years.
Whether I (and others) like it or not, Floyd is an ATG - who schooled Canelo. Makes sense to me that he'd want to go a little out of his way to fight an ATG, especially if he considered himself to have a real chance of winning. Canelo on the other hand has been beaten already, and holds only one title. Not quite so much of a big fish to fry, as such.