To paraphrase my opinion from back then:
- Easier onboarding, and a familiar, easier UX
- customizable feeds you can subscribe to + starterpacks instantly give you full timelines and people to follow (and followers, if you're in many starter packs)
- better discoverability, and therefore higher engagement
- stacking moderation and excellent security features (e.g. detachable quote boosts, "the nuclear block")
- many users who tried Mastodon first had bad experiences with "HOA"-like behavior and over-enthusiastic mods