Why wasn’t Rebecca Luker nominated for her Maria in The Sound of Music?

It did not win Best Revival. It lost to Cabaret. It only received one nomination (for revival because there were only three musical revivals that season). It was not that well received even though it ran for over a year.

Neither Luker nor the production were nominated for many awards at all. It just wasn't well-received and it was overshadowed in a season that also had Cabaret, Ragtime, The Lion King, and even Side Show. 

MaxineElliott said: "Mr. Wormwood said: "It did not win Best Revival. It lost to Cabaret. It only received one nomination (for revival because there were only three musical revivals that season). It was not that well received even though it ran for over a year."

Not well received? I’m just curious why. It looks like Laura Benanti took over for Luker before the show closed so maybe Tony voters didnt see her?"

The heck are you talking about? Of course the Tony nominators and voters saw Luker: She played in the show for more than a year and it was nominated for Best Revival (and the Drama Desks nominated its orchestrations). Benanti did three months as Maria after Luker left.

Laura Benanti was a postulant/ensemble member and Luker’s understudy in the original cast. She took over the role of Maria after Luker left a year into the show’s run. 

MadsonMelo said: "Betty Buckley got nominated for a flop show as the sole nomination of the show was either a big name check or Luker was in a really bad production."

Luker’s soprano voice singing those songs seems like a slam dunk. Mary Martin won the Tony for the original production so it’s just surprising she was passed over. 
 

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I was lucky enough to see this production! I was a child so wasn’t exactly discerning, but do recall being blown away by the sets/physical production and by Luker’s singing… I enjoyed it more than the movie.