1. The official Pixelfed app just has a nicer looking UI
2. There’s not really a competing app for people leaving Insta like there is Bluesky vs Mastodon
3. Pixelfed’s content is mostly visual so it’s easily digestible to casual users and you don’t have to scroll past dry Fedi arguments
4. Better discover features so users don’t have to do a bunch of legwork to find who to follow

Just my guesses though, but like any social media it really depends on if big creators will switch and if users stick with it over time

Better UI and a better discover page mainly. Plus it’s gotten a lot of organic advertising just from luck and people talking about it, and no obvious competitor like Bluesky