Some rudimentary efforts to do so have, on occasion, been made. While wholesale bots (i.e., no real-time human control at all) are totally incapable of performing at the level required to beat high-end raid bosses, certain simple, repetitive parts of the process can be automated with add-ons and macros.

There are two issues here: desirability and difficulty.

Desirability: if you automated those parts, then there wouldn't be a game. No one wants to just theorycraft for a while and then sit there and watch while things happen automatically. Theorycraft is the metagame. The parts where you actually execute the plan are the gameplay. And the gameplay is fast-paced, exciting, adrenaline-rush-generating, skills-demanding, and cool-looking. The excitement of the gameplay is what WoW raiders live for.

Or at least, most WoW players take this stance. Knowing this, Blizzard has consistently banned any game add-ons that go too far in automating things. There's a fine line, and sometimes it shifts, and sometimes it's blurry, but the intent is clear: thou shalt play the game yourself, not write code that will play the game for you. (As with all commandments, precise interpretation is a longer discussion.)

Difficulty: The reason you can't actually fully automate the steps in question (unless, perhaps, you are the game/boss designer, and have access to all the internal game variables) is largely because:

1. Positioning (i.e., location and movement of characters in the game world) matters a lot. (The reasons why are several, and probably boring, but take my word for this.)
2. Timing matters a lot. Which is to say, not only must character ability usage be timed correctly with respect to the behavior of game elements (monsters, environmental events, etc.), but players must also time their actions with respect to, and in response to, what other players are doing.
3. There are many variables that go into correct play. Combinatorial explosion would make automating this a daunting task. For a human, learning a boss strategy, or a play technique, is faster than devising and implementing an algorithm to execute it. To a human, you can just say "kite that mob over there, then release it when I yell on voice chat", and (if he's a skilled player) he won't need to be told twice. Writing code to do this... is likely possible, but not easy.