Despite the original mod being rarely updated, it is not discontinued and brings money to the original developer. The developer of CE could not contact the original one to discuss, if he is allowed to post the mod. When CE will become more popular, it will start "stealing" downloads from the original mod and this can cause problems. Unless the original mod will be discontinued officially, CE Forge will remain only on GitHub, not to compete with it.
Myrmexes in the original mod were very buggy, didn't work properly and sometimes caused crashes. The developer of CE makes this mod as a hobby and didn't have time to fully rewrite them, as fixing wasn't possible. Until he does it, he decided to remove the Myrmexes completely to avoid everyone asking him about bugs with them, as he is already aware of them.
It was decided by the community of this mod to let people choose between both of the ways, as the new one is much harder to obtain and many people loved Ice And Fire for giving good gear early on. The addon adding the recipes is in two versions, a datapack and a mod. It is developed by a separate developer, but is still semi-official and approved by the CE developer.