the chariot was its speed, which permitted it to drive circles around the phalanx, staying out of range while raining arrows on the foot soldiers. Once the latter had been thrown into disorder, it might be possible to put the chariots into formation, charge, and ride the enemy down.
Disadvantages
the problem was latter in the battle. When everyone is fighting hand to hand combat, the horses would run over there own army and kill its own troops.
My conclusion, given the paragraph given, is that the Belgians likely made the choice given rubbers value to plant rubber trees instead of food wherever practicable.