Why put in 3 round gears and a differential when one (precisely manufactured) larger gear is "close enough"? Technology does help, but commoditization is the enemy.
Which is truly sad since commoditization could make good things cheaper if mass produced. I want the future promised where stuff doesn't wear out but most people just want a cheaper one. If Lego can mass produce plastic bits that have tolerances of 2 microns then why can't other manufactures of higher end things do so. I mean people are willing to pay more for quality since for toys Legos aren't cheap but are very well made. Even on the secondary market a major selling point of bulk lots is stating that there are no Mega Blocks.
No amount of careful planning will ever replace dumb luck.