Because Mrs. Hudson is a stone-cold BAMF in her own right and deserves better than someone who has two secret wives. This takes place during the opening bit of Hounds.
Damn Sherlock and his bloody harpoon and his astute observations. Mrs. Hudson fumed silently as she stormed down the stairs and out the door, only to duck right back in to Speedy's next door.
"Don't you even start with me, Somnath Chatterjee." She snapped, before the sho powner had a chance to even say hello. "When, exactly, were you planning to tell me about your wife?"
A thin sheen of sweat cropped up on the man's forehead, and he pulled at his collar while pretending to fuss with a sandwich.
"My wife..." He sighed theatrically. "It was a loveless marriage. Arranged, you know. That was the custom when I was young. She thought it best if she stayed back in Pakistan while I-"
Her sharp glare cut him off. "Pakistan? I was talking about the one in Doncaster... You really are a pig. I tolerate a lot, Mr. Chatterjee. I tolerate you being late with the rent, I tolerate you banging against my wall when you get in here at four in the morning, I tolerate your overly loud radio until closing time..." He opened his mouth to speak again, but she just put her hand up and continued shouting. "I dealt with enough crap from my last husband, I deserve better this time around. I refuse to tolerate bigamy."