“Milk from a non-kosher animal costs more than milk from a cow so there is no financial incentive to do so”
Who is buy9ng the milk form the non kosher animal? The farmer is not selling it separately and he is not buying it,. However he may have non-kosher animals of all sorts on the farms that have milk and by mixing it in he can sell something he wouldn’t be able to sell otherwise.
One needs to be a Chochom besides being a Talmud Chochom to come up with a legitimate heter.