It's because killing a CEO of a megacorp is a nationwide signal for civil unrest. A lot of people want to see those with power be shot on the street. Virtually no one wants to see a random person be shot on the street.
Executions are somewhat less commonplace than random lethal violence. Plus, everyone knows how to reduce random killings, though we don't do it... this, on the other hand, is a problem requiring more attention.
Also, there are a myriad of channels on which $$$ people can donate to police departments (nycpolicefoundation.org https://gothamist.com/news/5-facts-about-new-nypd-commission... etc), but poorer people are not going to do that, so why bother spending as many resources?