Crocodile laid down like Katakuri did. He lost mentally more than physically. The bomb failed, the plan failed, his whole philosophy failed because of Luffy. Had to restart from scratch and think his whole shit through again. He gets his dreams back in prison thanks to miss golden week so that's why he got a buff in marineford and afterwards, because he has his haki back after losing it after jobbing to Whitebeard and losing his dreams.
If you don't think crocodile has haki in marineford, just explain how he clashes with Akainu without his sand melting into glass.