Belts?????
This would make more sense if we were talking about different colored belts, rather than what they are made from.
How about players on the same team wearing pants high or low? What about some wearing sleeves while others don't? When it is cold, some wear hoods, others don't. Some don't use batting gloves. Long hair, short hair, facial hair, clean shaven, jewelry, no jewelry? These, and many other things, are all more noticeable than what material the same colored belt is made out of.
So a team can dress like a team and still the players not look identical. In fact, it seems like the individual look is getting more popular in sports these days. Not saying that is good or bad, it's just very obvious.
Personally, if only four players on my team got a leather belt, I would rather have what the majority is using. And the only time I have ever noticed belts is when someone doesn't have one or if their's were a different color than the rest of the team.
Will admit... I like the identical look. Everyone with short hair, clean shaven, pants worn the same way, no jewelry, exact same look for every player. Unfortunately, that is kind of rare these days.