> the computer who goes first won more than 56 percent of games, suggesting that there is a notable advantage to playing the first hand [...] There’s no way to know for sure what specifically causes this advantage, but perhaps giving one player initial control of the board has some beneficial effect.

"What specifically causes this advantage" is, to put it briefly, playing first. The first player will have about 0.5 more opportunities to score. In fact, since it's legal to pass, it's a trivial game theory result that any advantage in Scrabble belongs to the first player.