1. They Very Rarely Live Up To Their Hype
A fundamental law of cinema seems to be that a prequel's hype is almost always greater than how well it's received. The hype and anticipation around a prequel to a highly regarded film series (especially one with a devoted fanbase) tends to outstrip its critical reception because the audience's expectations are set too high by what has come before. Which takes its toll on the prequel's critical reception because some audience members are disappointed by it not living up to their expectations or its predecessors. Star Wars Episode 1 can without doubt be called one of the most highly anticipated films of all time, to the extent that a comedy film titled Fanboys was eventually made about four fans trying to steal an early copy of it from George Lucas. So whatever George Lucas delivered (and I still maintain that The Phantom Menace isn't that bad) could never live up to the hype and anticipation that grew around it before its release. If it was an original film rather than a Star Wars prequel, it would probably have been better recieved. Not a cinematic great by a long shot but still okay. But since it was a prequel to one of the best film trilogies of all time and was so widely anticipated as a result of that, it was viciously received by many and comments are still being made fourteen years later about how it supposedly ruined Star Wars forever. Although The Phantom Menace is a bit of an extreme example, it still shows a trend that frequently applies for prequels. Some fans are so fond of certain films that they don't want to see what they consider to be something so excellent dragged down by a belated prequel. And since fans of a prequel's source material are the primary demographic for that prequel, fan apathy or disdain for it can hurt its success at the box office and its critical reception.
Do you think prequels are inherently flawed? Let us know in the comments section below.