The current "normal" was also added because old Normal was steadily climbing in difficulty since WOTLK. People who raided in WOTLK started hitting brick walls in later raids, as normals were approaching closer to heroic was previously.
Like... Heart of Fear normal was significantly tougher than a lot of stuff in ICC normal. And... DS normal was pretty faceroll for the most part.
Horridon normal broke a lot of guilds.
The bleeding edge players play at such a higher level than the rest of the playerbase, keeping things hard for them and then having normal be challenging to those not quite there, left out a lot of the playerbase that used to be doing fine until the difficulty creep.
Also, the stated intention was so that more social level guilds could get everyone involved in their raiding rather than benching people when it got too tough for them.
And Flex raid size came with it which is great.
https://www.reddit.com/r/wow/comment...flexible_raid/