What fighters specifically are we talking about here?

You have to understand that the majority of multi-weight champs are actually on their way to another division when they are fighting in one, and so can't afford to hang around.

Look at Manny, that guy fought everybody worth fighting in the featherweight divisions then wanted to test himself against the p4p best and guys like Oscar, Floyd and Manny.

The lightweight division was never anything more than a pass through, he was moving up in weight, got another belt on the way and has now reached his new destination with the Mayweather dream fight.

You can't have a go at him for not fighting the best at lightweight, that was never his intention, he was headed for Floyd.

I do agree in the case of Floyd Mayweather that he should have fought some legitimate welterweight opposition seeing as he has been there for years but most fighters who move through weight classes do so to get to a specific opponent, nobody has the time to clear out every division they fight in especially when half of them are just quick drive throughs on the way to where they want to get to.