[nimblegorilla]

It's true that the person with the most resources will probably win, but a key factor getting to that point is ability to best ramp up production to produce those resources.

Early in the game it is important to try to get that next settlement or city. If you can place a robber to block important sheep or whatever is in short supply then that can be better than just blocking a high number of pips. When placing a settlement sometimes it is better to spread out rather than circling around one hex with high pips (and being vulnerable to a robber knocking out your entire production chain).

Another aspect of placing the robber on an opponent's "high pip" space is that they become motivated to play soldiers and possibly move the robber to your own high pip space. If you instead place the robber on a ho-hum tile you might not block as many potential resources, but the robber will stay away from your tiles for a longer period.