Why so many entries on IMDb are incorrectly categorized in terms of genre

It happens all too often that movies and series turn out to be something other than what the genre tags on IMDb suggested. I get the feeling that the genre tags were initially assigned by someone who has only seen the trailer or the cover artwork, but not the actual movie or series itself: Comedies listed as thrillers, thrillers or dramas listed as horror, and so on. And to make matters worse: If someone who has seen the movie or series then takes the time and effort to submit a correction, it's usually first rejected with the reason "Unable to verify". A description of the content and how it complies with the genre definitions is often not enough - you also have to look for any web sources that mention what actual genre the content is in. If you have experienced this several times, as I have, you become discouraged from submitting corrections. The consequence is that the genre categorizations at IMDb are hardly useful anymore. It's more worthwhile to search for a movie or series on Wikipedia - there may also be mistakes there, but overall I've found that movies and series are more likely to have the correct genre designation there.