For a lot of hardcores its pure anti fun to be forced to split your raids to its maximum and farming m+ dungeons all day long. If you decided to play in a race-to-world#1 or race-to-wowprogress-page#1 guild, you cannot ignore a single opportunity. Unfortunately blizzard wasnt that economical with ingame opportunities this time.I can guarantee you 90% of top raiders do not want a tournament realm.
Raiding at a top level for the majority is only done because of the release when you finally kill the final boss. This means all the work you have done from beta to release night to heroics dungeons to mythic dungeons to split runs until finally you kill the final boss. Actually working hard toward something to be rewarded is what these raiders enjoy.
If you circumvent this process via tournament realm you lose all of the effort you put in. It loses its fun.
Furthermore that kind of raiding has changed a lot over the last years and quantitative factors becoming much more important than qualitative factors.