How come only 1 or 2 cartridge makers offer a tune-up after run in?

Sure it's great that Brooks Berdan adjusted the setup after a cart's suspension is broken-in, but isn't that different than what VDH does and actually opening up the cart and adjusting the suspension, rechecking channel balance etc. inside the cartridge itself? 
I also have owned a number of VDHs, agree with OPs observation that the adjustment or "tuneup" does improve the sound and was curious about other cartridge manufacturer's viewpoint(i.e. why it's not their practice) on that idea.Cheers,
Spencer

Perahps, there is better QC with modern cartridges which negates the need for a follow up tune-up, or there is not enough cartridge artisans within the manufacture to perform a follow up tune-up.   

@testpilot My understanding as heard from VDH dealers is that it isn't about QC, it's about how the stylus wear in the first 300 hours upon inspection let's VDH see how to adjust the suspension to make sure that on the table that's being used the cartridge will perform as close as possible to its design. Maybe VDH stylus vs. other shapes is part of the reason why they do it and others don't? Your last suggestion could just as easily be the reason...maybe someone else can tell us both. Cheers,
Spencer

Never owned one. Never read anywhere that this was recommended. Is this something a buyer finds out after purchase?

Just read the latest Crimson review in Enjoy the music and the reviewer covers this subject.