Brain Before Sleep

I looked it up on gemeini its necause the creaters of batman said they wanted to and his abilitys is base off of bats and hes not real and the creaters only make him like bats cause of that

It actually explains it in the first movie. Batman had a traumatic experience in his childhood that involved bats, therefore leading to him developing a lifelong fear of bats. In a later scene he was asked what he wanted his nickname to be, and he said the thing he feared most.