Usually a salesperson operates on behalf of someone who has something to sell. I have no financial interest in any of the three companies which hold licences for levothyroxine, nor the companies which actually make them.
And other treatments are, at least sometimes, available. Including liothyronine and desiccated thyroid tablets. The people I know who are taking thyroid hormones use all three.
I am well aware of the meaning of refining in terms of oil, metals, and numerous other fields. But despite your response, I am no closer to understanding refining the fluids within muscles.