They don't charge any more to get the color matched.
They want to sell you the paint,
instead of someone else selling you the paint.

When you do a color change, you have to do the inside of doors, trunk, etc
and THAT can be more hassle than getting the color matched to start with.

ooorrrrr........if doing the door jambs is too much hassle, and paint matching is too much hassle, a person can always buy used spray cans from the flea market
and have a paint job that everyone will call "unique"..... -Bob