Why do fighters use different make gloves?

I remember when pacquiao was made to use grant gloves against morrales and he blaimed his loss because he didn't use reyes(punchers gloves). Also I heard mosley was made to wear Grant gloves by floyd, why? Then in the khan-malinaggi I remember some1 saying why is khan using reebok gloves. So I have 2 questions: 1. Why do fighters use different type of gloves, afterall they are all made out of leather right? 2. If they are different what advantages do each give, like I know reyes are said to be 'punchers gloves', but what about grant,everlast,reebok etc.