I appreciate the coordination problem here, but I do think that states are making it harder than it needs to be. The federal government doesn't need to be involved. Each state can decide on their own how to coordinate this, it does not need to be the entire nation (and indeed it already isn't, as the examples of AZ and HI show).
Considering that one of the biggest problems in our country today is trying to run more and more at the federal level instead of at the state level, it's really silly to add to that pile.
Uniform time act of 1966 prevents this being set at the state level outside of remaining forever in standard time.
The federal government constrains what states are allowed to do, so it has to be decided at the federal government. AZ and HI got legal exceptions long ago.
No, the law is that states can decide to not implement DST at all, but they can’t decide to have it permanently.
At one point a couple New England states were looking at this, but for that reason it would have been implemented by moving to a different time zone: year round AST rather than year round EDT. (Which are both UTC-4.) That said, I think states need federal permission to move time zones, too.