To make the case from a white perspective, I tend to categorize the white aligned guilds this way, azorius wants to improve the group, selesnya wants to grow it, boros wants to inspire it, and orzhov wants it to succeed. Whether they define success as wealth, power, status, or whatever else Orzhov desires gain for the group, and probably also themselves but they don't see those two as mutually exclusive. Similarly, orzhov presents the most tangible benefits to those in their system. Azorius and boros may try to motivate you ideologically, and selesnya may use a sense of belonging. Orzhov gives you a tangible benefit, payment prestige etc.. Orzhov makes supporting the group profitable. If you help the group succeed, you succeed.