Fedibridge

As someone else mentioned here, these other centralized platforms often advertise heavily on subreddits like /r/RedditAlternatives, and they do seem to have some people on there. Does anyone know if they are attracting a lot of people or why people prefer to join other centralized sites before joining e.g. Lemmy? Are they a "threat" to the growth of fediverse platforms like Lemmy, Mbin or just experiments that'll fail sooner or later?