It's all about politics as usual. Chopping the Reds wouldn't save much and you can bet that the savings would never be re-invested elsewhere. Likewise, the Reds pilots maintain their proficiency whilst flying with the team (they get more hours than their counterparts) so it's not as if they would suddenly be "freed-up" to join other squadrons - in essence they're already there and available.
It's just another political gesture - the Treasury could be seen to be saving money even though they'd save little and just destroy another Great British Tradition. Nothing new there then...