Yes, that is the issue. You see, if the birthdates are posted publicly, then when player A beats player B, player B's dad can make the excuse that player A is a certain age. Or, if player A is a 5-star in the class of 2015 and player B is a 4-star in the class of 2014, player B's dad can tell everyone that player A really ought to be in the class of 2014, in which case he would not be ranked any higher than player B.
If the age is a secret, then the age basis for excuse-making and *****ing and whining and putting down other players is not there for everyone to see.
Thanks for my laugh of the day............and as they say, the truth is often told in jest!