Harry Potter fans force relocation of £430m undersea cable to avoid Dobby’s ‘grave’
(www.theguardian.com)
First, it's only a measure that people consume the media, not that they enjoy it. Hate-watching is a thing, as you can tell from a comment higher up. Or they watched because someone else wanted to watch (or they thought someone else wanted to watch).
Second, enjoyment does not reflect quality. People can like bad media. I like the second D&D movie, and even I can only rate it's quality as "fine".
Third, even at the height of its popularity and among its strongest fans, there are flaws galore in the books. Even ignoring the racism, sexism, ablism, slavery, "ugly is bad" mindset, and all that, there's also stupid plot decisions and lazy world building. Of all the fanfics on AO3, well over a third of them are fix-fics.