I have been using Mastodon for a couple of years now, and while the privacy focus is part of the shift, the bigger shift is understanding that Twitter and Mastodon are not competitors. PixelFed and Instagram are not competitors.
The old platforms are social media. They are entertainment platforms that nominally connect you to friends. But their actual customers are advertisers and entertainers (influencers?)
The new federated platforms are social networking. They're community-owned and operated for the sole purpose of serving a community. They don't have customers, they have members. They are collaborative efforts run by individuals and not-for-profits.