PeerTube uses ActivityPub because this federation protocol is recommended by the W3C and is also used by other projects like the social network <a target="_blank" rel="noopener noreferrer" href="https://joinmastodon.org/">Mastodon</a>.
Read the <a target="_blank" rel="noopener noreferrer" href="https://docs.joinpeertube.org/maintain/configuration#scalability">scalability guide</a> if you plan to have many users or viewers