Because...
Gen 2
18The Lord God said, “It is not good for the man to be alone. I will make a helper suitable for him.”
19Now the Lord God had formed out of the ground all the wild animals and all the birds in the sky. He brought them to the man to see what he would name them; and whatever the man called each living creature, that was its name.
20So the man gave names to all the livestock, the birds in the sky and all the wild animals.
But for Adam
f no suitable helper was found.
21So the Lord God caused the man to fall into a deep sleep; and while he was sleeping, he took one of the man’s ribs
g and then closed up the place with flesh.
22Then the Lord God made a woman from the rib
h he had taken out of the man, and he brought her to the man.
23The man said,
“This is now bone of my bones
and flesh of my flesh;
she shall be called ‘woman,’
for she was taken out of man.”
That's why.