Why do restaurants charge for plate sharing, and would you go to a restaurant that charged for it?

I read a review for a local restaurant and someone pointed out that they charged $6 for plate sharing. To me, that’s a cheap and greedy way to treat a customer. I plate share with my daughter all the time. I also will give what I don’t eat to someone at my table (obviously someone I know well, who won’t mind), as I may not eat much of it and will be happy to have someone else have it.

Why do restaurants charge for plate sharing, when all it means is one more plate for the to wash?

Do you go to restaurants that charge for plate sharing? I have seen it discussed on menus, but I do think $6 is excessive.