[THe_Silencer]

You can ask the same question about why most of the manufacturers don't properly shim their gears. Time=money and due to the loose tolerances of most airsoft parts, it'd would take to long for them to carefully shim, correct AOE, grease, check compression, adjust motor height, etc. since every airsoft gun is made slightly differently. Short answer is they don't care enough to take such measures, as much as I wish that every stock aeg I open up come perfectly shimmed and greased.