Because they don't break the rules as they are (workarounds exist, e.g. by going through facebook's external redirector https://www.facebook.com/l.php?u=), and the mods think having high-quality original sources is worth the tradeoff: https://news.ycombinator.com/item?id=15531085 (Which is a comment on the specific example the OP mentioned)
Comments
I think what I've seen previously is people just flag the articles until they're removed.
I wonder why they haven't banned wsj urls by now
Because they don't break the rules as they are (workarounds exist, e.g. by going through facebook's external redirector https://www.facebook.com/l.php?u=), and the mods think having high-quality original sources is worth the tradeoff: https://news.ycombinator.com/item?id=15531085 (Which is a comment on the specific example the OP mentioned)