Anyone that is interested in discussions on either defederated community, will create an account for both.
And that is the reason why reddit is still growing. If you are required to make multiple accounts just to engage with the communities you want to engage with, Lemmy is no better than separate forums. And those all got overshadowed by reddit for a reason.
The fediverse keeps sabotaging itself with instances defederating left and right, that way it’ll never become an alternative regular user would want to join.
And that is the reason why reddit is still growing. If you are required to make multiple accounts just to engage with the communities you want to engage with, Lemmy is no better than separate forums. And those all got overshadowed by reddit for a reason.