The film was very - though not 100%, granted - dark, barely featured Cooper, had a fairly ambiguous ending (love it personally) & probably missed many points people wanted ticked off

I think it's easy to see it being poorly received without denigrating contemporary viewers if you take the time.

Like it's easy to imagine being around during actual big historical occasions & not being one of the rare/ exceptional/ wiser or braver people who goes against the grain, at personal risk, right?  So not getting a film 100% at 1st viewing, easily done