If I was sparring and was getting blasted to the body and naturally dropped my guard to cover my liver/ribs and got cracked hard because of it and someone asked me why it happened. The answer would be "I wasn't guarding my face because I was busy covering my body." That is an answer to WHY something happened.
Pettis said he went into defense mode after he lost vision in his eye, he didn't say "Well if my eye was fine I would have fucked him up" or anything like that.
Sure, you do get beat up in this sport, but there are reasons WHY you got beat up and it's far more interesting discussing the whys and hows instead of getting butthurt every time a fighter notes factors in the fight that cost them.