> I am seeing so many apps and games making replicas to gain momentum. All they do is just change name. Why Apple and Google allow this ?

They probably don't strictly "allow" it in many of the cases cases that occur, and neither does the law. The issue that the store owners aren't able to effectively actively police it, and it relies on the vigilance of owners of the original apps to identify and complain of violations. And even most app owners have more productive uses of their time than hunting down every clone that might break the rules.