The explanation they always give for why we can't craft the best gear is because they don't want players to be able to get fully geared just by buying stuff from the MB. Yoshi-P wants people to be able to get the best gear in the game without ever using the MB.

Personally, I disagree with this vision of his. The best gear in the game should function like abjuration gear in FFXI. One part of the gear comes from a non-tradable boss drop and the other part comes from crafting. It's stupid that the best gear in the game can't even be melded.