I think it has to do with the fact that when you say judge, you usually atribute a bad conotation to it. Even the phrase "I misjudged you" is usually used as a form of saying "I had a bad opinion of you, but now I changed my mind", rather than when you change your opinion from good to bad people put it more like "I'm dissapointed in you".
It is true that there is both positive and negative judging, but because the ward "judge" sounds like something bad or that one shouldn't do, you atribute the negative judging to it, wile positive judging is defined more like "forming an opinion". They are sinonims, but the way you say it gives a different feeling.
I hope I made myself understood, I'm really bad at explaining
