I was wondering the same thing myself.
I found that if we turn this into a holding game, then 7/2* 6/2 becomes the preferred play (see below). In the original position, there's more contact and both sides are somewhat inflexible, and the 3pt is better for blocking White's straggler as well as for any blot-hitting contest that might materialize. At least, that's one theory.
       
 
          
 | | White is Player 2
score: 0
pip: 150 | | Unlimited Game | pip: 127
score: 0
Blue is Player 1 |
|
| XGID=--a--bECC---cD---c-b-b-b--:1:-1:1:54:0:0:0:0:10 |
| Blue to play 54 |
| 1. | XG Roller++ | 7/2* 6/2 | eq: +0.422 |
| Player:
Opponent: | 73.18% (G:8.56% B:0.14%)
26.82% (G:3.30% B:0.09%) | |
|
| 2. | XG Roller++ | 8/3 7/3 | eq: +0.381 (-0.041) |
| Player:
Opponent: | 71.40% (G:9.29% B:0.20%)
28.60% (G:4.00% B:0.10%) | |
|
eXtreme Gammon Version: 2.10