If by "manifestly" you mean "in your opinion, and despite a lot of critical acclaim."
This is true of a lot of things, though. Take Shakespeare's comedies. They aren't funny. A modern Shakespeare audience laughs at the jokes even though they already see them coming (having read the play multiple times already). This is the opposite of normal experience. I won't laugh much at a genuinely funny comedy if I've already seen it 10 times, so why would I laugh at 500-year-old puns that I've heard before...when even the best puns rarely cause laughter the first time?
And concerning "getting published and selling today" - Sarah Palin gets published. That doesn't mean that what she writes is anything other than trash.
I've seen the film Animal House[0] about 20 times and still think it's funny. Part of the humor is the set-up and delivery. Yes, I know John Belushi is going to force potatoes out of his mouth, but when it happens it's still funny because of all the little details.
Same for A Night at the Opera. Dated in some ways, but hysterical in others. Grouch Marx is just funny, even when you know the jokes.
Now, my wife wonders how I can watch the same movie twice, since I what happens and how it ends.
My brother, though, compares this to listening to music; you know the words and how the melody goes, but you still like listening to a familiar song. Some people are that way with books and plays and movies, too.
[0] Yes, I am that old.