Zeller constantly being condescending to Will throughout s1 while he slept with Lounds and leaked enough info to obstruct an active investigation is so hypocritical of him… It only took Will being acquitted for him to come around – well, his playground style nitpicking is not not understandable. Still, glass houses and throwing stones and all that. All of us, even the most self-aware, have some quantity of Zeller in us, that’s the funny(?) part.
It could also be that Zeller was afraid of Will. Instinctively, I mean. Will’s brain works in a different dimension and Zeller must have felt enough discomfort with the “unknown” quality in Will that he forgot to be empathetic towards him after all.