Another key to the scheme is that money/loot from the late comers is given as payment to the early comers. In ff programs, miles are miles, whether you earned them long ago or today (indeed, in some programs they expire).
That reinforces my point. Redeem your miles early because the longer you wait the more diluted they get.
The airlines know, miles they sell through third party are profit because 60 % (guess) will end up never redeemed. Miles given to loyal customers and frequent fliers will almost certainly redeemed. Thats the reason they want to hit us with restrictions like delta - no crazy routing, etc.