They might have been in the Middle Colonies just close enough to New England to worry that it might catch on, though. Since there was probably a movement toward seclusion before it was official, I could see a few deciding to emigrate before, on the (probably correct) assumption that they wouldn't have to bother if they ever did make it law back home. Those might have been hanging out in, say, New York when the Salem trials happened, and gone, "Oh hell, not here too! Maybe it'll stay confined to the Puritans... hopefully... maybe hiding a little more thoroughly isn't such a bad idea after all, though." And then after the Statue, I agree about the inducement for more magicals to come to the colonies. (A couple may have eventually run off and joined the Indians if they found an amenable nation, as some Muggle colonists also did - even further out of the Ministry's reach.)