Did you know that the Department of Veterans Affairs ran out of money during the government shutdown of 1995, and had to halt operations? In 2009 they lobbied for a law, which passed, that funds their budget *two years at a time* so that it's unlikely to happen again. The president at the time said this law “ensures that [this department] will no longer be held hostage to the annual budget battles in Washington.” source:
So now, other government services are lobbying for the same exemption. For example, in 2019, Senator Merkley proposed doing the same thing for the Indian Health Service, and his bill (the Indian Programs Advance Appropriations Act) passed in 2022 after years of lobbying by Indian groups. Thus that service is also one of the “essential services” that may continue operations during a government shutdown.
Basically, every government service has an incentive to lobby Congress to put them on the list of "essential services" so that government shutdowns don't affect them. And thus, nowadays, government shutdowns just don't do much.
Advance Appropriations: A Victory for Veterans | Vietnam Veterans of America
