Eh, old man Philip already had a wife for about each finger; typically ranking aristocrats from the families of assorted clients and allies.

And that would just be the formal mates.

A perfectly normal way to do politics those days. Until very recently marriage was, after all, nigh universally a socio-economic-political arrangement between families - if the partners actually liked one another, that was a bonus. Alex's spouses rather stick to the pattern, especially when you consider the politics he was dealing with - marrying into the old Achaemenid line gave him at least a veneer of legit claim to High Kinghship and helped align diverse Persian aristocratic houses with him, and ditto for Roxanne (after Bessus was dealt with the remaining Persian resistance was centered in the eastern provinces of the empire, and led by a Bactrian nobleman; establishing concrete dynastic links with suitable potentates of the region was an obvious way to help pacify the area and earn some degree of loyalty).