I can't speak for all creampie fans but here is my take...
IN PORN:
It really does nothing for me to watch cum run out of a girls pussy. It's the idea that the girl is letting him, usually a stranger, cum inside her. That is the ultimate form of submission.
The more guys dumping inside her the better. The dirtier the girl the better. To watch the load run out is only proof that it happened.
There are a lot of fake creampie sites out there now, and true aficionados can tell a fake from a real one. So can you... check for the ones that don't convert or re-bill.
IN REAL LIFE:
I don't even want to pull out. 1) It feels incredible to pump inside of a raw pussy while you're cumming. 2) Again, the submission thing and dirty whore factor if there is more than one guy.
However in real life, I don't want a single drop to dribble out. My sperm is precious and I want every single soldier to stay inside her. Even better if she does not clean it out, sleeps with it in her and I do it again in the middle of the night or in the morning.
Sperm is supposed to be deposited in the vagina. To NOT put it there is going against the laws of nature and the universe.