What is the most likely reason that chromosomes must line up on the cell equator before being divided and moving to the opposite sides of the cell?

This process is called the mitotic spindle which begins to develop during the prophase. The reason why chromosomes must line up on the cell equator before cell division is “to enable the microtubules to attach to the kinetochores properly”. The microtubules then form the network that will later pull the duplicated chromosomes separately.

 to enable the microtubules to attach to the kinetochores properly