[Siegmund]

Doesn't seem overly surprising to me.

When everyone at the table (or all but one person at the table) is dealt a bad hand, board cards don't get dealt at all from "enriched" stubs. When many people are dealt high cards it's more likely that at least two of them will want to fight over a pot, and force a board to be dealt from "depleted" stubs.

The effect is probably much stronger for aces than any other rank, since between 1/3 and 1/2 of ace-high hands are worth seeing a flop for one bet while less than 1/4 of K- and Q-high hands are.

This is part of why it's so hard to directly address the "poker is rigged" complaints since a simplistic experimental design will falsely accuse a fair game of dealing too many 'bad' rivers. (And broadways on the river will tend to help the person who was already ahead with his TPTK, while small cards will either be blanks or complete straight and flush suckouts.)