Max and Elsa songs: "How Can Love Survive?" And "No Way To Stop it"

I am currently in a production of The Sound Of Music playing Max. I was watching the movie to do further research on the character and found that him and elsa's songs are often cut from productions. Why is that? I find that they play a vital role in the story particularly No Way To Stop It. I've often heard it's due to Eleanor Parker being unable to sing in the movie but if that's the case then why not just dub her? They dubbed Christopher Plummer and Peggy Wood. I just want to know why these songs are cut.