Why did Tommy Hearns fight Hagler's fight?

The short answer is because Hagler was on his ass and he had no choice.

 

I think that Tommy Hearns abandoned his strategy because of Ego. Hearns was used to devastating his welterweight opponents and 154 lbs opponents rather easily, Pipino Cuevas and Roberto Duran. Also Hearns must have figured that he wiped out Duran much quicker than Hagler had as Marvelous Marvin had struggled with Duran, going the distance with him in Nov 1983. Also Hearns figured on jumping on Hagler to make him respect him. Hearns strategy failed on the night of April 15 1985, as he was stopped by Hagler by KO 2.

 

It's funny because I feel Marvin was better than Carlos, more skilled, hit harder , even though shorter matched him in reach and chin ... but Marvin's weakness was self doubt while Monzon was supremely confident ...

 

It always was. Personally I never liked excuses in boxing. Most fighters when they lose have excuses created by ego and in a way it is a good thing to have, it gives them excuses for losses and then they can ignore the loss and keep winning and fighting, whether the excuse was valid or not-usually it is not as much as we think. As for fighters when they won they were the best ever.
Tommy had some good excuses for Leonard and Hagler- he had weight issues in the Leonard one fight coming in too light and overtrained, and Hagler fight his legs weak because of being massaged. Yet when he beat Benitez, Duran and Cuevas earlier he was tiptop. Duran made a lot of excuses when he lost also. Benitez never trained was the word. It is a common thing. Tommy's problem was he brawled and put his all out but he got tired and Marvin was so motivated to prove how great he was and in this fight he did. Marvin earned that win by coming in and being decisive something as someone pointed out here could be a problem for him. In many of his top fights he was indecisive like with Duran and Leonard, and it meant losing rounds.

 

Loose lips sync snips.