Currently only Issue 3 of Sonic Eggs uploaded, we will be bringing the old issues back in the future.
I always believe that characters need a set reason for their personality. Sonic is arrogant because everyone loves him. Knuckles is always angry and bitter because his whole life is centered around guarding a giant emerald and being alone. Of course it would upset him to see Sonic squander his good fortune of having close friends.
Knuckles will be getting a good reward (temporarily) and be an important part of the story later on.