Another difference is that they don't see a political motive.
I agree that there was an anti Mormon motive, but I doubt it was the ONLY motive. The reason given, his breakup with a Mormon girl friend. was obviously years ago as he is married with a child. Some reports suggest when with the girlfriend, he actively sought to convert, but was angered because the Mormon church would have required getting rid of his tattoos.
The media was complicit in creating a narrative that Charlie Kirk was killed by the left, some like Stephen Miller actually saying Democrats. Yet the killer never voted nor did they cite any examples of activism. It is pretty likely that the ONLY issue he agrees with the left on is LBGTQ+.
In contrast, the Michigan killer drove around with an anti Biden flag and had a Trump sign. Unlike Robinson, he IS overtly partisan. Where the right has blamed us of using inflammatory language - calling some of them fascists, as they do fascist things, I seriously doubt a week has gone by without at least one hateful social media post by the President which is then repeated by the media. Could THAT anger have triggered the attack by an unstable man, who at least in the past used meth?
Consider that it mostly was Kimmel suggesting that Kirk's killer was not a leftist that led to their anger. It was important to their narrative that it be seen as their enemies killing the Christ like Kirk. Reality was far different, much of Kirk's own speech was hateful and the killer grew up in a very red, gun loving family.