Dylan Roof did get charged with hate crimes and was convicted on all 33 counts, leading to a death sentence. Stacking terrorism charges on top of that would have been pointless.
Mangione, by contrast, is getting charged in a state without capital punishment. You need the terror charge to make this a First Degree Murder case. Otherwise he's looking at parole after 15 years.
"They're making us CEO's afraid, terrified even, so he's clearly a terrorist. The implication that the working class could actually fight back against the systemic oppression we inflict on them? That's horrifying. We can't allow them to believe they could ever fight back. Make an example of this person."
They used to be terrified a lot more often when history was closer to JFK, Mussolini, Lincoln, and the French Revolution. When the leaders really thought the punishment for bad leadership was their ass, they gave a shit more.
As long as the action terrorised a large enough group of people it's terrorism, it's just this time, the terrorised people are the rich cunts hiding in their mansions like the traitorous cowards they are.