Besides Roger Moore's age, why is AVTAK so hated?
I'm getting the whole thing regarding Roger Moore, who was in his late 50s at the time, being "too old" to plausibly play James Bond anymore out of the way, since that's the most obvious statement.
AVTAK itself, generally regarded as one of the weakest Bond movies and I think, even Roger Moore himself has considered it his least favorite among his personal canon. Moore in particular, hated the scene in which Christopher Walken psychotically and manically guns down the hapless mine shaft workers with a machine gun.
I recall reading Leonard Maltin's review and even he started right off the bat in saying that AVTAK is one of the weakest Bond movies. He singled out Christopher Walken for being a "bland villain", Grace Jones for being a monotonous villainous, Tanya Roberts for being a "wimpy" leading lady, and wrapping it all up with the criticism that the movie "goes on forever".