Could be a number of factors. After the Mugabi fight and maybe even earlier, Hagler was thinking about retiring, which is the first sign that a fighter's heart isn't 100% in it anymore like it used to be. Then you have a guy coming back from a 3 year retirement, a welterweight who had retired because he felt he "didn't have it anymore" and of course was forced into a medical retirement before that... and here Hagler is an absolute monster at MW, just destroying everyone he puts hands on... it's pretty easy to get overconfident there. And of course you have to give huge credit to SRL, who fought a great fight.

In the end, I have to go back to Hagler's decision to fight orthodox for the first 2 rounds and essentially give those rounds away. If he had fought southpaw and won those two rounds, he picks up the SD. If he won at least one of them, it's a majority draw, he keeps his title and there's probably a rematch. To this day I wonder what the fuck he was thinking to not come out southpaw.