it should be noted that these bans are community bans, not instance bans. your title makes it look like people are getting instance banned from lemmy.world, while the examples you've shown are about community bans.
if i'm not mistaken, several/most of the lemmy.ml bans/ban complaints have been about instance bans, which affect all communities on the instance.
this is by design. actor ids (unique identifier for accounts) should not be reused due to undefined behavior for how other instances will deal with that.
if you want to have a more technical explanation, https://socialhub.activitypub.rocks/t/reuse-of-identity-channel-addresses-revocation-reissue-of-keys/2888 does a decent job at explaining some of the issues with this.