[2019] Why must I repeat all five waves in Altar of Sorrows but can repeat Waves 6 and 7 only for EP?

It’s already bad enough waiting for a specific day for each weapon and then having terrible rng when it comes to the curated drop (that blasphemer still eludes me).

Why would Altar not be formatted exactly like EP and have it so we only have to complete Wave 5 and the final nightmare upon each successful completion? It makes it extremely frustrating when I spend a significant amount of time finding an instance with enough players and then having to complete the entire event only to get a terrible drop and start the process all over again.