Well nobody really expected any UN “troops” to actually stand and fight in the first place.
Those blue helmets don’t exactly strike fear into the hearts of terrorists.
They aren’t really there to fight. They are there to occupy a buffer zone between the antagonists reducing the possibility of inadvertent fighting, and to be observers that can testify about who shot at who. Their presence also somewhat complicates planning for making an aggressive move, as they will have to be bypassed.
They are very lightly armed. In this case it is a bit unusual in that the Filipinos and the Irish defended their positions and shot back.
They might not have been issued ammo. After all, they were up against the Religion of Peace.