upward curve rubs girl in the rght spot during missionary. think about internally on the back side of clit. this is an area that can be rubbed aand help for penetratve orgasm. no matter how huge you are most women, like almost all, need cltoral stimulation tobget off and cant do it on penetration alone (without a lot or practice). some can never do it..kind of like a guy having orgasm only rubbing prostate area (behind the balls to ass). yes, its also possible to cum like this but most men could never do it without stimulaing their dick head some too. same for women and penetrave sx.
long story, up curve some can be great for woman. this area is how women can learn to squirt too. they def get more wet if yourub it while working the clit.
some people also just lke the look im sure. better to be curvered up than sideways imo.