Because the theaters are dark on Monday nights.
When I was too young for kindergarten, this record was always on the turntable. My mother adored Julie Andrews; I knew this even though I had no idea at the time who Julie Andrews was, other than that she was singing on that record. (I was little enough so there was a lot I didn't understand. The concept of the Cockney accent had to be explained to me before I could follow a word of Eliza's songs, and I can recall there being a discussion about God as bearded guy who sits on clouds, the upshot of which was, "no." The simplified version for preschoolers didn't include that the bearded, winged guy Al Hirschfeld had drawn was George Bernard Shaw.)
Other things I didn't know then: Julie Andrews had been a sensation in Britain as a child singer, had been cast in The Boy Friend on Broadway in 1954, the year I was born and she turned 19, and in 1956, became the star of Lerner and Lowe's Broadway hit, My Fair Lady. By the time I was trying to parse Cockney phonemes, she had moved on to the London production and had defined Eliza Doolittle to everyone's satisfaction.
Imagine my mother's outrage, then, when the big splashy Warner Brothers movie version, released in 1964, starred Audrey Hepburn as Eliza. This had been the evil work of Jack Warner, the film's producer; he decided Julie Andrews had insufficient name recognition to drive a big film. Adding insult to injury, Audrey Hepburn didn't even sing her own songs. She was dubbed by the talented Marni Nixon, as were a lot of actresses of the time.
In our family, we do not let go of this sort of outrage just because of a little thing like the passage of 50 years, so, for our amusement this evening, let's revisit the "who deserved that movie" question. (In fact, in a rare case of more or less letting go of what she regarded as a terrible injustice, even my mother was satisfied with the outcome when Ms. Andrews pronounced herself satisfied -- but I'm getting ahead of myself.)
Our friends, the tireless posters of musical-theater YouTubes, have done extra work for us to isolate a single point of comparison between the two performances: the singing. Not who looks more winsome, or more convincing as a Covent Garden flower seller; nothing really to do with Audrey Hepburn at all.
The first video below, of Eliza's first song, Wouldn't It Be Loverly, is the un-tampered-with scene from the film, itself a composite performance with Marni Nixon singing and Audrey Hepburn lip-synching. The second segment, however, is the same video but with the Julie Andrews audio from the original cast recording swapped in. So: both times, Audrey Hepburn acts, but two different people sing.
Marni Nixon vocal:
Julie Andrews vocal:
Ultimately, of course, there's no way to "settle" the question of who would have been "better". The movie was what it was, and Jack Warner can't really be called wrong to think that so expensive a picture needed an established movie star to guarantee its success with people living far from major theater districts. The controversial casting left Julie Andrews available to star in Disney's Mary Poppins, which was an enormous hit and the year's top moneymaker (My Fair Lady was #4). In early 1965, when both actresses were up for the Golden Globe Award for Best Actress for their respective films, here's how the canny Ms. Andrews handled it.
In the subsequently-awarded 1964 Academy Awards, My Fair Lady won eight Oscars, including Best Picture, and Best Actor for Rex Harrison. Audrey Hepburn was not nominated. The Oscar for Best Actress went to Julie Andrews for Mary Poppins. And my mother smiled.