This is one of those things that non-teachers don't entirely get. If you work in an office, time is pretty flexy. If a meeting can benefit by running an extra 10 or 15 minutes, you just do it. But in most schools, when the bell rings, you're done. There is no little extra bit of time you can just throw into the work.
The Common Core is not a national curriculum, because it is not a curriculum at all. It is only a set of standards, and that's completely different from the scope and sequence of curriculum planning. But like that terrible Match.com date you went on, the standards/curriculum distinction only looks good on paper.