The lack of humor rather fits in with Superman's character. He is noble, benevolent and selfless - but alien, a continual outsider who idealizes humanity and never seems to be capable of recognizing their true nature.
I never felt he was meant to be funny in the comics and so often comes across as eerily polite, otherworldly and untrustworthy*.
All of which make him an excellent character, but not the buffoon people expect him to be.
*By which I mean that humanity places so much trust in him, that his mere absence from any situation is viewed as a betrayal. Superman has made people so reliant on him being there that they have unrealistic expectations.
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