It's also just a great way to show how much you enjoy raw breeding. Obviously I want the load fucked into my hole, but gently sucking the wet dick is a good piggy way to enjoy the seed more completely and show respect while you're both having fun too
I've taken some really great breedings from guys who aren't 'conventionally' attractive. Get those loads, that's the goal, we're not having a beauty contest later
If the top cums deep inside like I always ask, the next best way to experience the seed is to suck him (gently) after he pulls out. Shows appreciation and respect, he was generous enough to give you the nut