What I do think are the main good things about the #fediverse and #Activitypub (and I don't think the often-cited lack of algorithms and no-data-harvesting are the key things):

• ability to choose your host and its set of rules (different things are important to different people; you can select a server that matches your values. It isn't about more or less moderation, it's also different kinds of moderation)
• ability to self-host (e.g. if you want to post a lot, maybe a lot of videos, you may find it problematic if someone else bears the burden of the storage costs. With self-hosting you can do what you want without guilt) (it was recently pointed out that organisations can host on their own domain, providing an alternative to a blue tick verified account system)
• mix of different types of platforms (you can follow and reply to videos on a YouTube-like service, or photos on an Instagram-like service, with your Twitter-like account)

Why is better privacy and no algorithms, and no ads, not the main advantage of the fediverse? Because that's just the current culture. There's nothing technically stopping someone from having ads on a server, or introducing algorithms for top-posts, or collect usage data. We just collectively don't like people who do that, so no one is likely to do this anytime soon.