"Kimmel didn't call for violence. He may made fun of Kirk and Trump"
That's not how I see it. Kimmel purposely lied and uttered slander against Trump/Maga by suggesting the Kirk killer was part of Maga. That could mean legal implications for Kimmel's employer -- such as the FAA dropping their broadcast license, or possible lawsuits etc.. That combined with Kimmel's low ratings was probably a very easy business decision for ABC to make.
This is not a first amendment crisis. He attempted to defame Maga and was fired by his employer. No one said free speech was free from consequences. If I mouth off under my company's banner and they don't like what I say I'd likely get fired too.
Edit... and the reason it is not a first amendment issue: Kimmel, now unemployed or self employed could go tell these same 'jokes' on a street corner or on a podcast or even his own venue, and probably nothing would happen in terms of being 'cancelled'. He may not have any advertisers, or may not be on an FAA controlled medium, but he could say what he said. Therefore, I think it was 100% a business decision for ABC to cut their losses.