Most aftermarket paint is not applied and cured as factory paint was applied and cured..
Factory paint has been tested and approved to higher standards than some paint sold at automotive paint supply shops..
Yes, they have the Factory Pack paint too, but that doesn`t mean the body shop is going to pay the higher price for it and may instead get a less expensive paint that will do the job just fine.. But it might not wear as well, last as long, etc., as the original factory paint that had been applied perfectly - including with the necessary agents at the exact amounts - to insure longevity, some degree of UV protection, etc..
In my experience with non stock paintwork, it is sometimes really done very well and sometimes its not.. It will also have a tendency to lift right off of especially plastic parts, because the plastic was not prepared properly for maximum adhesion...
Dan F