Chess:
1 move has about 30 possible ways to play.......

Backgammon:
1 move has about 21·X possible ways to play........
This X is about 8 to 40 and depends on the position. For looking 8-plies/4-moves ahead it would need for X=35(in a simple middlegame position):
(21·35)^8 = Oh my God!
So no minimax or alpha-beta would help.........

Note:
21 is the number of different possible rolls.
X is the number of different possible plays for a single roll of the possible 21.