That's because the facts are on the side of the Tyrannosaurus rex, and it's hard to debate from a disadvantage on the side of actual paleontology.
The Prequels, on the other hand, are viewed subjectively. One person can think they're the best damned creation of cinema since Humphrey Bogart and Ingrid Bergman shared the stage in 1942. Another can think that they are an abomination and should've never been made, and every copy should be destroyed. They're both right and both wrong.
Personally, I think parts of The Phantom Menace (Basically all of Darth Maul's scenes, and the Trade Federation invasion), parts of Attack of the Clones, and the entirety of Revenge of the Sith were pretty good. The hate for the prequels is, frankly, overstated, overdone, and overrated. They weren't the best by far, and admittedly were pretty bad, but nowhere near as bad as some people think.