That's like asking why there are so many different chains of fast food joints.
Different ways to get the money from the potential customers.
"OUR [product] is not just DIFFERENT from the others. It's BETTER!"
Little FISH come forth knowing how to SWIM.
Little SPIDERS come forth knowing how to excrete WEB material.
But little HUMANS come forth NOT knowing which of the several thousand Goddesses and Gods actually exist, and which are the products of human imagination.
A REAL "Intelligent Designer" would have taken care of that, IF it was an important thing.
So, either there never was an Intelligent Designer, OR it's not important which Belief System anyone subscribes to.
MANY Goddesses and Gods, just a FEW, or NONE at all: Makes no difference.
Just be NICE to each other.
And if there IS a SuperThing handing out rewards in some "Afterlife", you'll get a nice one.