I imagine it's possible, but "no reason" is definitely a stretch. The parts of DC that are federal land are hardly contiguous, and trying to force a clean split between DC and Maryland looks like it would be a nightmare: https://www.washingtonpost.com/graphics/local/dc-marijuana-m...
you wouldn't have to be perfect. You could carve out just the contiguous core. I believe this was floated by Jeff Flake. Federal buildings can, in general, exist on state land.
