There's nothing unprofessional about it. It's just far less greedy than
the old-style business model for wedding photography, and it's easier to
manage.

It's hard for me to think of a reason why I'd want to keep wedding
negatives. I don't try to shaft clients into paying me exorbitant
prices for prints, so I have no reason to prevent them from making their
own prints, and in fact I facilitate this with a contract that grants
them a generous license to use the photos in just about any way they
want (although I keep the copyright and a few rights), plus digital
files and/or negatives. Wedding photos typically are worthless except
to the family that commissioned them, so why keep the originals?

It has nothing to do with screwing people out of money. It has
everything to do with quality control.

If I give someone my negatives, they'll go to a non-professional lab to
have prints made. While I doubt that Wally World can handle 2 1/4
square negs, any non-pro lab will make prints that are substandard in
quality. Somebody will look at them and think, "Jeez - those look like
crap." When asked who took them it will reflect negatively on me. Not
good business.