if we can take insulin from pig why cant we take pancreas of pig to replace into human

Pig Pancreas will create major immune reaction in the host body. The host body will not be able to accept it as its own.Theinsulin from pigs is purified which reduces the chance of the insulin user developing a reaction to the insulin. There are still chances of immune reaction against it.
But now we have recombinant insulin which is expressed in E.coli and then extracted.