I've thought the same way for a long time, but people always argued that it would leave behind everyone outside of progressive areas.

Which is true, but well what's the alternative? The bureaucratic hurdles of a federal government are too immense for it to be fully responsible to people's needs, even when you don't have a government which is perpetually locked in a stalemate at best.

Grassroots movements by definition need to start at the municipal level; and leaving everything up to the federal government in a top-down approach is what paves the way for centralization, consolidation of power, and the resurgence of fascism.