Someone cleverer than wot I am guv will probably answer this in a more eloquent way but I'll try my best until they come along.
The answer lies in the traffic orientation scheme (TOS) along, or rather "up", L10.
As part of the standing agreement between us at MACC and the ScACC Antrim sector boys and girls we stick traffic on the northern edge of the airway on a radar heading - not straight through the centre (you should be offset from the IOM VOR by a little not heading dead for it).
Conversely the Scots will do their damnedest to plonk traffic inbound to our sector (the West/IOM sector) on the southern edge of L10. This way everyone is nicely separated - TMA outbound climbers on the north from TMA inbound droppers on the south and so on and so forth. Somewhere in that mix/mess we also have to squeeze overflyers in each direction at anywhere between the base of the airway and FL240. So a lot of headings are sometimes required to get everything set up in a safe and orderly manner. And to ensure noone drifts off outside CAS.
So that'll be why you'll eventually end up on a heading of 315/320 or so on your way up L10. And coming the other way, more often than not, you'll be on 135/130 towards the south.
This doesn't happen with the MALUD/CREWE routing as no such TOS exists per sé, which is why you'll get direct MALUD and then plonked onto a heading against traffic coming the other way or traffic joining the mix at WAL.
Dublin do, at times, try to put traffic inbound to the sector on the southern edge of L975. This isn't always necessary though.
Hope this helps a little and we're always glad to have flight crew visiting the place if you fancy seeing it all in action.