Users are trapped by the network effect and a desire for ease of use over anything else.
The corporate alternatives will always be an easier sell.
Twitter > Bluesky
Instagram > Upscrolled
TikTok > RedNote
Reddit > no corporate alternative
YouTube > no corporate alternative
Discord > no corporate alternative
To get the average user, you don't just have to convince them to leave Twitter, you have to convince them to leave corporate social media and all of their friends that still use it.
You have to convince them to accept additional inconvenience any complexity (@usernames and @instancenames?) in exchange for no direct, tangible benefit. (We know it's worth it, but the average user doesn't know and doesn't care.)
The people who could handle that are already here. Adoption going forward will be (at best) a slow trickle until we reach some level of critical mass.
Why people don't leave Reddit
Reddit has the advantage of years of community-built knowledge, and it's a "one-stop shop". Looking for the gaming community? Go to reddit, type in blind, it'll be in the top 3, if not the top 10.
Go to the threadiverse, and you have to run the gauntlet of servers (what's an instance?), deferated instances (why can't I see XYZ?), and 20 communities with similar names (which gaming community is the "real" one?). The switching cost is too high for most as long as Reddit still exists.
Why people don't leave Discord
Discord is easy to set up, and they're digging their claws into game dev by making it easy to monetize communities (enshittification, here we come!).
~~Revolt~~ Stoat isn't federated, so each server is segregated from the others. As they grow, users will centralize for the sake of convenience. My bet is they either sell out or remain a niche alternative.
Element is (still) too complicated and unreliable. Audio sharing is inconsistent (no audio streaming on desktop screenshare, mics won't work, etc). Video calls aren't fully implemented.
::: spoiler Why people won't leave YouTube No one can match YouTube's sheer scale. They have billions of videos and billions of users. Their monetization system means that creators are identified to create quality content for the platform.
By contrast, PeerTube's best content is often mirrors or backups of content from other platforms. PeerTube is a great backup, but without monetization to incentivize creators, it's not a real alternative.
