Why not? Married people share just about everything else in their life, sometimes including bank accounts with real money. Sharing a MMO game account is probably one of the least significant things they share in their lives, so it was probably an entirely natural thing for them to link both POL accounts to the same SE account, seeing as it lead to easier management of both accounts.
Not only does this make sense to do for married couples, but also if you are a parent, paying for game access for several kids. There's no reason to prevent one of the linked accounts from participating in events when they have a perfectly fine reason to link them, other than being a completely square person without any ability to be flexible or understand other people's side of a story.