Why are biotechnology companies eager to design genetically modified organisms to express therapeutic proteins, particularly ones that would otherwise have to be isolated from blood products (e. g., human antithrombin) or animal organs (e. g., insulin, originally isolated from pig pancreas)?

This is because of reasons of-

safety,

cost-effectiveness and

 difficulty in  accessibility of needed  protein

Explanation:

In order to reduce cost of production for maximal profit, bio.companies usually design their production of therapeutic proteins  in possible  cost -effective way.This is to  ensure maximal yields from production sales. Therefore maximum cost  effectiveness is achieved through GMO rather through isolation from blood products or other sources which are expensive and capital intensive to get

In addition safety concerns during production is of ultimost importance to theses companies.Therefore when   using  of protein from different sources  high safety measures are needed to be put in place to achieve best results. whereas GMO comes with little risks.

These companies experiences difficulty in collecting required amount of low abundant protein needed for the synthesis of therapeutic proteins, thus they will rather prefer the design of GMO for abundant supply.