The thing that makes these quests particularly annoying in Classic is that you can't even be sure that you are in the right area. If you can't find any mobs, it might be because:
- You are in the wrong area. Classic directions are often somewhat vague.
- You might not get close enough to the mob to detect it. This is especially true if you are under-leveled.
- Someone else may have come through just before you and killed the mobs, so you're waiting for them to respawn, but you don't know that.
In retail, the minimap displays the area where you can find the mobs. So at the very least, you know where to search.
In Classic, there's just too little information, and that makes the whole thing a frustrating exercise. These sort of quests really need something to offset that loss of information. For example, a tracker that told you if you were hot or cold.
Or possibly if the geography was constrained to make finding the mobs easier. For example, stealthed mobs in an underground mine or complex. Here you can traverse the corridors, and be reasonably certain that you've found or not found any mobs in the paths that you've already taken.
But stealthed mobs out in the Classic open world are just overly frustrating.