Apart from because 'somebody with the right rank said so' I don't understand why we eternally complicate our procedures with nobody apparently correlating the slight savings today versus the long-term loss of hearts and minds. Apparently minor things like this all add up to final straws, requiring markedly more long term expenditure to replace people who have had enough of this nonsense.
So much more could be achieved in terms of savings by issuing a flat rate no matter where in the world you are. As a long term investment people working extremely hard wouldn't think they were being screwed over again by the organisation they're representing.
It wouldn't be so bad if this change fell into line with other organisations like the Civil Service, MPs etc. Of course MPs make their own rules and certainly don't want to be pestered by actuals - think I read the other day a MP gets a flat rate for every night away from 'home' (doesn't matter if this is at the London 'residence' though - that's a second home hardship they have to suffer). Civil Servants benefit from a union and don't take kindly to nonsense.
Our 'representatives' didn't get where they are by disagreeing now did they?