Having more complex rotations would make tanks and healers incapable of doing their jobs. Even if Yoshi P thought OP's request was a great idea, he wouldn't implement it because it would require rebuilding four expansions worth of content around healers and tanks doing an expanded number of things the game wasn't built for them to do.

All the fights in the game are scripted with timed beats requiring you to use the appropriate healing/mitigating skills at the appropriate times. To whit, you're too busy for much else. Adding complexity would mean needing to change all the current content.

And there's no reason to do that because the game is wildly successful. Most tanks and healers are happy with it.