Because undoing a death sentence if it turns out the culpit was one level higher in the corporate chain is pretty hard.
I agree in principle that IF your country has the death sentence, there is no reason why it should not be applied in such cases as well. But I think death sentences are problematic. Put them in jail and bar them from ever running a company again. That should be enough.
Some places don't execute mass murderers either.
There are plenty of arguments around this. For example, based on the crime rates in places with death sentences, I'm not sure it provides as strong a disincentive you think it does.
... but they're in suits! (nah joking burn them in hell, they are all bunch of power hungry sociopaths, normal folks wouldn't survive a day among such C-suites due to being decent human beings).
But realize that list for whatever action would be done would be... very long. Monsanto, bunch of Wall street guys (if you trace actions to real consequences), this and probably many more. I think life sentence in maximum security prison in US would be actually worse.
Also, you soon hit grey area, say defense industry and its bribing of government to start wars that killed millions... where do you draw the line? One's man patriot is another's murderer
Why? If you knowingly decide to poison thousands of people, that makes you a mass murderer. Since when are we so lenient about those?