Why can't we (states) ignore clock changes without the federal government? The federal government doesn't seem to care about standing laws.

19 states have "no more changing the clocks" laws passed, but aren't allowed to do so without approval of the federal government?

It's pretty obvious you can just do what you want these days, consequences are trivial to non-existent, so why don't we just not change our clocks? (or change them and not change them back, whatever floats your boat)