Because they're interested only in killing and defense of the hive. There'll be later information gathering sheens for whom that'd be appropriate. I'm fine with just Listen and Spot.
though I guess Spot and Listen would be useful out of the range. However, I like tremorsense and blind-fight better also.SRD said:The creature usually does not need to make Spot or Listen checks to pinpoint the location of a creature within range of its blindsense ability, provided that it has line of effect to that creature.