Steven Paddock didn't randomly target Mandalay Bay, he deliberately targeted Mandalay Bay (MGM Resorts)
Just because Paddock tried to book rooms at the Life is Beautiful concert doesn't mean shit.
Casinos break promises all the time.
You thought you had a comped room, free food, etc. but at checkout they decide to bill you for everything because you didn't lose enough money. There are plenty of cases where casinos have fucked over players on comps. This is a very good motive that police didn't want to focus on.
