Unfortunately this topic has not been able to draw conclusions. Do we have the whole story behind each closure? Probably not. Is IHG just telling people a line, "Because of signing up for promos you were not targeted for" whether it is true or not? Probably.
Obviously just signing up for promos targeted for others doesn't sack every account that has done it.
Searching other forums for the stories behind closed IHG accounts brings up serious offenses: selling free nights, using multiple accounts so one person is earning repeat points for the same promos, things that would close any frequent flyer or hotel loyalty account.
Stories about brand new accounts being closed for signing up for multiple promotions may be true, but that is not something most of us with 10+ year old accounts need worry about.
I simply can't see IHG shuttering accounts which contain a JP Morgan Chase free night certificate paid for with the credit card annual fee-- no big bank would go along with that kind of behavior and have to deal with the calls about people demanding their $49 back because their accounts were closed because they entered in an online promo code? Never happen.