It probably has something to do with the accuracy of the mold making
process. I mean where are you going to get a mold that is within a fraction of
the wavelength of light. Do you understand what 1/4 wave or 1/8 wave means? We
are talking millionth's of an inch here folks!

The only way to get this done correctly is grind and polish and test
that is how it is done. In the end everything has to hand retouched for the
final figuring. Machine made optics don't cut it for Astronomical purposes. The
reason being no one has ever been able to program a random stroke only humans
are able to make randomenous work to there advandtage. The reason you want
random strokes is this is how you avoid zones!

May I suggest some reading material. Amatuer Telescope Making Books I, II,
and III these guy's have all the info on what it takes to make an optic
including testing

Clear Skies
Dwight L Bogan