Also, that people who have twenty years to plan for their retirement to happen under these conditions will not be as screwed as someone told that their plans for next week are off.
But those people retiring from 2040 are still getting screwed by a policy. How is more time to prepare gonna help? Are you gonna magic some more money out of thin air by then?
Hence only doing this for future pensioners will give equal time as reitred.
(at least, this is the core reasoning)