Why no Emmy for Lead Actor/Actress in a Variety Series in the 1970s?

There were so many acting Emmy categories in the 1970s. I don't really understand why Roots was placed in one category (continuing series?) while other miniseries competed in another, and telefilms were in yet another. In fact, I don't understand why a guest acting performance by Beulah Bondi in The Waltons beat Leslie Uggams's excellent work in Roots for a lead actress award. Yet there were many weird Emmy wins (in albeit weak fields) until the Emmys devised separate awards for guest acting. Until then you'd see a guest star win a Lead Actor/Actress in a Comedy/Drama Emmy for shows as diverse as Taxi and The Incredible Hulk.

So how come, with all those categories, there were no Lead awards for variety series in the 1970s? Essentially, it would have gone to Carol Burnett and Flip Wilson every year, but still, it makes little sense why there would be supporting awards for Tim Conway, Harvey Korman, and Vicki Lawrence to fight over (alongside one-time guest stars and the stars of their own one-time specials), but Carol Burnett or Flip Wilson could only win if the show were to win.