Manny lost because he's now old, slow and fighting a much bigger younger dude...
Crawford won because he's young, more skilled and just as strong...
It's the style sometimes and not the age of a fighter and sometimes not the skills of a certain fighter that beats an all time great.
Manny lost because Horn has a great chin and Manny has no defensive movement, he only puts his gloves to his face and takes power punches and uppercuts and then taps his gloves smiles and attacks you, making you think you didn't hurt him, if you don't believe me watch the Cotto fight when Cotto hurt him and watch all of his other fights.
Crawford outboxed him easily and didn't have a scar and didn't even get hit, because Crawford has better defensive footwork and moves his head and clinches when being attacked, then times Horn coming in and lands power punches.
Crawford uses defensive movement and footwork and then clinches to not get hit with clean power punches, like Whitaker, while Manny uses footwork and gets trapped on the ropes and covers up while getting hit with power punches that are clean and he's getting hurt.
Mayweather uses footwork and defensive shoulder rolling while not getting trapped on the ropes sliding off and turning his opponents, then clinching and holding and only stays on the ropes trying to set traps and tiring his opponents out, like he did against Cotto and other pressure inside fighters.
Manny doesn't use these types of defensive techniques, like Whitaker and Crawford even while being a southpaw fighter, because it's not his style and wasn't taught to him, he was only taught quick movement backing up and when on the ropes cover your face and try to block punches.
Horn beat Manny taking advantage of his defensive style and using constant pressure making Manny fight every round, because Horn can take his power punches and fight even harder while Manny is covering up taking power punches and then trying to hit Horn and Horn is using foot movement and jumping in and out like Ricky Hatton attacking Manny and hurting him or stealing rounds with constant pressure and movement.
Crawford took everything Horn does and did to everyone else he fights away and destroyed him stopping him late in their fight.
If Manny did the same thing Crawford did he's still the champion and stops Horn just like Crawford did. But Manny doesn't have the boxing ring IQ to adjust and pull it off, unlike Crawford and Floyd does.
Spence is your seek and destroy you, body punching power puncher, while using little footwork and movement, standing his ground and taking heavy power punches, then stopping you. Spence is basically a clone of Terry Norris, but with a better chin, until he's actually tested against a superior talented boxer skills wise like Floyd, Crawford and other all time greats.
Brooks was actually giving Spence trouble and in my eyes winning the fight and others had it extremely close, until the knockdown and eye damage happened.
Crawford will make Spence miss and pay and use quick footwork, while countering Spence and clinching him and Spence will be trying to knock him out but can't, getting frustrated and losing a close fight by 2 rounds or just getting outboxed easily, but the judges making it close.