All you can think of is that the IFR clearance is not available because of conflicting traffic (having told us that you can't have E without radar) ---- but it is beyond your imagination that, just perhaps, the most common problem is that the centre frequency is not available on the ground.
If this is one of the places that has E almost to the ground, what happens here when the conditions are less than VMC and the aircraft cannot get a clearance? They just wait until the weather clears up?
Cheers,
NFR.