Because there are a lot of individuals who will say IV-VI are incredible, masterful and flawless and then talk about how cheesy, terribly acted and inconsistent the PT is, but in all honesty, the acting in ANY of the SW films was never it's strong point, cannon is just always being retconned, and they're incredibly cheesy - people take their love of the original universe created and blow it out of proportion. Star Wars is in original and very rich story - one like never seen before - but some people (it's a small group, but it exists) will call the OT flawless and the PT nothing BUT flawed, simply because the "OT" is the "original" trilogy.