Who are you playing?  If you are Tarth, or used a custom with certain scouts they will not get attacked by monsters.  I typically play challenging and the shrills are one of the more common monsters that wander and attack, even troops.

It can be pretty random what the monsters do, what level are you playing?

***challenging****good lord, way to read.  Challenging is suppose to be even.  If you play lower than challenging than the monsters do not attack you as much.  Challenging seems to be the break even point.  As one of the people who thinks the monsters completely ignore the AI and seem to be an extra faction against the player, I am not sure.  In the games I play, I seem to get attacked all the time.  Pioneers, Armies, reinforcements moving to army, outposts, cities---they all seem to be fair game for monsters.