Why was Cicero killed during the proscriptions of the Second Triumvirate?

Cicero was killed during the proscriptions of the Second Triumvirate primarily because he was a staunch political enemy of Mark Antony and sought to undermine the triumvirate.12

Following the assassination of Julius Caesar, Cicero delivered a series of speeches known as the Philippics, in which he fiercely attacked Antony and urged the Senate to declare war against him. Additionally, Cicero attempted to manipulate Octavian to serve the Senate's interests against Antony, famously remarking that the young leader should be "given praise, distinctions—and then be disposed of".31

When Octavian, Antony, and Marcus Aemilius Lepidus formed their alliance in 43 BCE, they utilized proscriptions to eliminate their political opponents and seize wealth. Cicero was placed on the list of the proscribed, and he was subsequently murdered by a centurion acting under Antony’s orders. His head and hands were later displayed on the rostra in the Roman Forum.1243