What did they expect? A hit?
I call movies which preach, "message movies." Maybe you do too. And I don't like it when Hollywood expects me to pay my own good money to be told what I "should" think . . . . . about ANY particular subject. For instance, the 2008 remake of "The Day The Earth Stood Still" was just a mishmash of mumbo-jumbo with a prolonged ecology theme (which we've all heard 1,000,000 times in our lives).
So why did these filmmakers think anybody would pay to see big stars argue about gun control? Why are people surprised the movie flopped and they recouped less than 25% of their investment? What could it do but flop? And most important, how could they not realize that gun control is boring?
Why is gun control boring? Because it doesn't work and it never has. Criminals don't obey the law. (P.S. Canada just repealed its uniform national gun control law, which was very restrictive and placed huge demands and restrictions on law abiding citizens. It had been in effect a full 10 years. It cost the government vast amounts of money. And all of it was wasted because it never solved a single crime or resulted in a single criminal prosecution.)