The last thing 1st Platoon needs is a fucking gungan there, fumbling the grenades, 'oopsie, meesa fucksa up de plastica explosives!' and god knows what else. ;)

Besides, it was a Gungan senator that sold the Republic down the river and handed Palpatine huge emergency powers. Doubt they're popular. 

"Whoopsa, meesa fires a short round from de mortatingy!"