I think they didn't hate Guede because he was quickly (and relatively efficiently) locked up - so they didn't have anything to push against in that respect with him. In addition, I think many pro-guilt commentators rationalised that Guede had sort of in a way "manned up" to his involvement (even though in reality he did absolutely nothing of the sort - he merely tried to invent a story to minimise his guilt which still fit all the solid evidence against him).
I think they didn't focus on Sollecito so much because a) his story and photos were featured in the non-Italian media only a tiny fraction relative to stories and photos about Knox; b) he almost exclusively communicated in Italian, which added an extra barrier to many pro-guilt commentators; c) maybe because of (a) and (b), Sollecito didn't appear to them to be "flaunting his freedom" to anywhere near the same degree as Knox.
And I think they directed most of their anger, bitterness and vitriol at Knox because of all of the above. And in addition, it was easy for them to pigeonhole Knox in the "mean girls" category - that was something that was culturally familiar to many of them: the entitled, spoiled, reasonably-attractive brat who is a bully and a manipulator, and who is always dodging responsibility for her actions.
And lastly, I strongly suspect that for many pro-guilt commentators, Knox formed a strong figure for the projection of their own inadequacies, rages against the system, feelings of disenfranchisement and lack of control, and even unresolved traumatic episodes in their own lives.
I think (genuinely) that sociologists and psychologists (and probably also psychiatrists) would gain some real insight from studying the pro-guilt community in this case.