>because success in war could determine their advancement or even survival

It was also prestigious to have a well-equipped unit, much like it is prestigious to have a Mercedes today. So there was a kind of competition between the wealthy in this regard.

(Not only in this regard. House slaves from rich households often wore so lavish garments that there were legal attempts to get this under control; the nominally poor, but free Roman citizens resented meeting well-dressed slaves in the streets.)