Sorry, landedoutagain zooker is correct. If you went POL - ROSUN you would get uncomfortably close to someone holding at MIRSI as you entered the hold, even without overshooting it , hence the route to BURNI and the right turn there is to keep you inside Controlled Airspace and away from Warton/University Air Squadron who play out to the West.
Whilst the clearance limit is the holding fix you'd be amazed how many pilots don't hold especially when they come over to Approach near the fix! The usual answer is "Nobody on the last frequency told me to hold" - they usually seem to head straight for the MCT which can be interesting.