Profit is revenue minus expenses. Supporting more versions of iOS essentually means greater expenses. So the decision to drop support of older iOS versions is b

Profit is revenue minus expenses. Supporting more versions of iOS essentually means greater expenses. So the decision to drop support of older iOS versions is basically the questions of whether or not the additional expense of supporting it is greater than the additional revenue those users generate. For a company like Facebook, the revenue is much greater than expense, while for a smaller company, it's probably smaller.