Because the system rounds 5% or less of UTXO down to 0%, and rounds the rest up to the next 10%.  So to get 100% UTXO you need 20 BBP * RAC * .901.  In User BBP's case that would mean 1,301,683 * 20 * .901 = 23,456,327.66.

This has been discussed repeatedly, and while I personally think the system needs tweaked just a bit, that is the way it is currently coded to work and has been since PoDC Staking began.