End game "random" pairings

When the game is near the end, and players start dying off, certain players will be paired vs "ghosts" as we all know. But I wonder if this is truly random, and if not, what is the algorithm? I ask this, because since I started noticing I wasn't getting ghost matches, I have counted over 25 time in a row that I have not gotten a ghost. To the point that I don't think it's actually possible for me to be ghost paired. Why?