Edelbrock E-Street vs Performer RPM Heads

What I don't get is why do we have to get the aftermarket heads checked out for valve job, guide fitment, etc. and why are they not ready to bolt on OOTB?
Other than changing springs that match your cam, why do they even have to be touched or checked at all?
That is something that has always irked me.
Is their quality control that piss poor, or do they not even care?
They must be just literally slapped together on old misadjusted equipment or by assemblers who don't know or care a lot about their customers.....