The reason Jedi wear robes is to blend in, or to not draw attention. If you notice from the movies people do not recognize them immediately just because they are wearing robes. This must mean that this is common apparel.
These robes keep them from being exposed in harsh climates where they may be required to serve the order.
I guess that tactic doesn't really work in this game though, as everyone you meet goes "oh hey, master jedi, I'm honored, now help me with this thing over here". Everyone recognizes you, even on backwater planets like Tatooine!