St. Ignatius Loyola, the founder of the Jesuits, never wished for the members of the Society of Jesus to have any distinctive garb, as did most other religious orders of the time. His idea was that the Jesuits should wear the dress of a "priest in good standing" in the locale.
The Constitutions note that the clothing we wear should be "first...proper; second, conformed to the usage of the country in residence [or "not altogether different"]; and third, in keeping with the poverty we profess." [Const. 577]
Elsewhere, in what are called our Complimentary Norms, it states plainly "there is no specified habit." His thinking seemed to be that Jesuits would dress as other priests did in the region, out of a sense of modesty and poverty, and in solidarity with the rest of the clergy. ......................
There are plenty of good reasons for a distinctive religious habit.
First, it makes the question of what to wear rather simple. (And with a habit, there's less of a need to do much clothes shopping.) Second, it is a sign to the larger world about the very presence of men living in a religious order. Third, it ties the Jesuits back to all those who wore the habit in centuries past. Link (here)