Normally one might ask why would Yeonbeum do something else risky and pointless as deceive Changsoo, since Changsoo is a brute, so he would have likely love to keep working for Yeonbeum anyway, even after his mom was okay. However, Yeonbeum's character is exactly like that: he enjoys making people suffer, while he can watch from the sides and enjoy the show, seemingly innocent. So, as useful as Changsoo was to him and his criminal businesses, he still couldn't help it: when he saw the opportunity, he needed to make Changsoo suffer unnecessarily.
That being said, the hospital must have a corrupt doctor for this to happen. Perhaps it's a physician who's enjoying visiting Yeonbeum's brothel. I have a feeling the whole hospital will indeed close its doors before this is all over. Though we might never see it, if the series has Yoonsung switch to the next target.