Well, there's other issues people don't talk about with welcome thread.
Someone may come on new, not post an intro in the welcome forum, and people would piss and moan about them not posting an intro, even though no intro would add any relevant details to their question at hand. And if the idea were that if they posted an intro, they'd more likely stick around, that wasn't happening. They'd eventually get their question answered and leave regardless. Forcing people who are transactional to post there before answering them doesn't make them any less transactional, they still just leave after they get what they want.
But it seemed like to me that some used the existence of that subforum and someone's lack of posting an intro as an excuse to be a dick. Though, that wasn't a terribly common behavior.
I've also seen on forums before where someone, particularly new people, will try to immediately boost their post count by posting in every welcome thread no matter how old and irrelevant it's become.