Any b2c product I build has huge incentive to share the product, creating more users.

In the product itself, social is part of the value. So the more they interact, the more value they get. Similar to any social network you see today.

I do this a number of ways, none original. Reactions, upvotes, achievements, streaks, creating summary videos (like Spotify year in review), public recommendations, etc

Not OP but there are more than one ways to tap in to the distribution channels that exists thanks to influencers (Instagram, YouTube, TikTok, Twitter, Substack, Telegram). I, personally, don't see it any different than Nike hiring Lionel Messi or Uniqlo hiring Roger Federer. Where Nike is a global company, indie developers (especially the ones in Software) are smaller and thus could focus on just the right content creators, ie rely on marketing to boost sales.

This phenomenon isn't new. The book The Long Tail posited (way back) that even niche software could make millions now that the Internet had made it cheaper to reach just the right audience.

Teenagers, Zach Yadegari (calai.app) and Blake Anderson (apex.inc), who built million dollar app-based businesses in 6mo, plan to release a book on it: https://x.com/zach_yadegari/status/1845842051314614681 / https://archive.md/xXf9a