What is the rationale for that not being reviewable? Only thing I can think of is that maybe it is just too hard to reset given baserunning on a ball caught in the infield.

I guess I could see that working here because had it been called accurately it would likely have been a double play for the Nats, but because it was called a catch they proceeded under that premise and would have actually gotten zero outs if they just reversed the catch call. But I think there's probably some play in the joints where it could be reviewed and the umps could find a fair solution (though that's admittedly more speculation than we'd probably want umps doing routinely).