Maybe he wants to impress the visiting managers and a possible TV audience. Also, there is a chance that the bigger clubs can underestimate teams from a lower division. If the bigger clubs play away first, they are often satisfied with a draw, or even a small defeat. They know they will do their job when they later play at home. Also, if one of the teams have a clear lead from the first leg, they can afford to draw or even lose the game as long as they win combined.
Some days offer few games to bet on.
Don't bet just because you feel you must. Search Database Statistics shows a clear advantage to the home team. If a team have hired a new coach recently, the players tend to perform better in the next game or two.