You just aren't tracking the discussion and don't understand the legal process.
It's the criminal justice system, fucko. I teach criminal justice.
The DA's office is responsible for nothing other than processing and prosecuting people who are charged by police/judges/magistrates/other law enforcement of committing crimes. They do not make the law, they enforce it.
The State Senate makes the law through legislative sessions in the same way that the Congress of the United States does.
The two are not related - the DA's office and the State Senate. They do not work in conjunction with one another.
If the State Senate says "this is the law, and this is the punishment for it" then the DA has no choice but to pursue that punishment for that crime.
I hope I've dumbed that down for you enough. It's painfully obvious that you never made it to high school, let alone graduated from it. The DA's office is not capable of "making" or "interpreting" or "add libbing" the law. That is all done for them by the State Senate. Any deviation from that would result in charges against the DA, his/her office and staff and all responsible.
For more, read here:
https://www.fclca.org/news-a-resources/lifecycle-of-a-bill.html