The mistake they make is trying to centralize all the costs of hosting a group.
Relay-based groups on Nost don't assume that, it is just a group where anyone can run anything (mostly group admins but they can offload to some to enthusiastic members) *while staying compatible using nostr events* (signed and standardized) .
You can imagine plenty of sustainable models in this setup, and you get the network effect benefit.
Simplex wants to run on a platform model to capture value while not being the central point of failure.
This is unfeasible.
