Corps are an alien life-form. They are permitted to kill without themselves being killed in return or in retribution or as punishment. They are an abomination.
And they are the product of a fluke of legal-economic history.
I agree, I think it would be very reasonable to instate the death penalty for corps. It's difficult though because they've already identified legal structures that make them very difficult to kill and even more difficult to kill in a way where they can't reassemble. Identifying an effective way to truly and permanently kill a corp, so that the death penalty would make a real difference, would be a good start.
And they are the product of a fluke of legal-economic history.