Because that's where they read it?

Yes, but you'd think they'd have enough awareness that most people on HN don't have paid subscriptions to WSJ which defeats the whole point of posting something to share information.

On the other hand, the submitter gets to signal "I read the WSJ and pay for a subscription!" to HN.

That's not very useful for anyone else on HN is it? It's gotten to the point where I'm tempted to petition that sites with pay walls just get banned.