were already dead to begin with (this was apparently the price they had to pay in order to travel across dimensions from their own parallel-world version of Hydaelyn to ours, thus they were basically just corporeal spirits.). Hence why it was so easy for Goddess!Minfilia to take them back to the First Shard, they were
just beings of aether by that stage anyway just like she was.
However we are not, we're still alive and have not achieved that stage yet (interestingly becoming a being of pure aether is what mastery of the Echo actually achieves so whether Evil!Derplander and his friends actually were not really 'dead' but had simply attained that mastery over the Echo to transcend themselves and were simply parroting lies told to them by Elidibus or whether they indeed died physically only to have their spirits pulled away from rejoining the Lifestream of the First Shard is unclear - there seems little distinction between the two concepts in any event, or at least, that's how it seems to me.).