Because people will pay a premium before committing the blasphemy of "gasp" mixing lines. And everyone kind of decided en masse that "Classics isn't MP" around here about in 2010 or so... As someone who primarily collects Classics myself, I couldn't abide paying a premium for an inferior figure of the same character. I'm guessing if more people were like me, you wouldn't see such high prices. But maybe that's not true. After all, many think that G1 originals are "worse" but pay top dollar for them. In collecting, the rarity and historic value of a figure is often more important than the quality of its sculpt and all that.