When a woman is sexually aroused, her vagina naturally lubricates and expands to take the cock. Over time, if her sexual partners have big cocks, her vagina will stretch and expand to take the largest of cocks.
Black men don’t just cum in a woman’s vagina, they get it in deep, past the cervix, and put it directly into a woman’s uterus. When they make a woman orgasm, it makes her vaginal walls contract and squeeze and milk his cock, and causes her cervix to alternately open and close and spasm and suck the cum in her vagina up into the uterus.
That’s why a black guy with a big cock will always get a woman pregnant before a small penis white boy. It’s just biology.