Some people are working on that. Calckey will soon be able to import posts from twitter (can alerady import from mastodon). Pixelfed can already import from instagram right now!!
Kbin and lemmy are very late in that regard. You can’t even migrate your social graph.
@fediverse
@rozno @SuperSpruce
Choosing a server is often the hardest step. That’s why you should send the signup page of your fav instance to your friends and not the official lemmy page.