“should have adequately known some psychopath was likely to come in guns a blazing?”
In this case, yes, because Cinemark had a no forearms sign which means they knew there are people with guns out there that they were afraid of and demanded they do not bring their guns into the theater.
Please, a no firearms policy does not turn into you should expect someone with them to target your establishment. This was a stupid lawsuit to bring, especially when Cinemark offered them a settlement, their own attorneys told them to take it, and the families refused and went to trial and LOST.
You don’t have to like the outcome, but clearly the families involved here made many bad decisions, and are now paying the price for it.