Could be down to state laws. I cannot find anything on the books in MD that says an installer must give you a choice to retail the SRECs. In fact, found this PDF put together by the state that talks about considering who gets to keep the SRECs while choosing an installer:
https://energy.maryland.gov/Reports/A Maryland Consumers Guide to Solar.pdf
Also an interesting point in the guide: "If you don’t own the SRECs that go with your solar energy system, you can’t claim that the electricity you’re using comes from solar panels. In that case, your panels are generating renewable
solar electricity, but effectively, you’re using regular electricity from the electric grid; whoever owns the SRECs is using the solar electricity your panels generate."
I always thought of the SRECs as a recognition of the additional value of the positive externalities generated by renewable energy, but at least legally that doesn't seem to be the case.