Mayweather is quite a bit worse than McGregor given his history of domestic violence. Awful scumbag of a man.
Everyone basically accepts that though so him being racist and misogynistic just confirms what people already know to be true, not exactly a newsworthy event. Whereas McGregor actually has a reputation to damage given so many people think he's basically a decent person behind the trash talk persona.
It's also a bit different given that McGregor represents Ireland in a way that Mayweather doesn't with America. That's something McGregor has actively courted with his constant reference to his country and countrymen throughout his career. Which is fine, except that means his fights (and his behaviour) get a different type of reaction in his own country. For example:
http://www.independent.ie/sport/oth...reland-during-this-weeks-circus-35931273.html
http://www.independent.ie/sport/oth...ter-and-no-one-batted-an-eyelid-35928001.html
Again, that isn't something Mayweather has to deal with when he behaves like a prick.