I grew up with people having natural colored teeth. People with artificial teeth color were those with false teeth. I find myself gradually getting used to it, but initially it did look like these people had quite serious dental problems: a problem bad enough to require all their teeth be replaced by artificial dentures. This is not attractive.

I have the same reaction to perfectly straight teeth or teeth without canines. It looks like false teeth. Crooked teeth isn't a good look either, of course, but forcing out all natural variation just looks like someone's had a problem. Uncanny valley: like someone with a synthetic flesh on their artificial hand.