Well, one reason for that (at least on the East coast) is that it doesn't really matter what you file, you will get something different. So why bother figuring out a routing you won't use anyway.
NORDO

That's not a reason. You will get a clearance, and you need to reject a
clearance you can't fly. But figuring out a route you won't get doesn't
address the route you -do- get.

Jose
--
The price of freedom is... well... freedom.
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