Cultural expectations in the real world.

Wired:why are voice interfaces female

https://www.wired.com/2015/10/why-siri-cortana-voice-interfa...

A related issue is the voice used in aircraft warning systems. Different aircraft use a male voice (Boeing, Airbus) or female voice (McDonnell Douglas). There's various contradictory research on whether a male or female voice is better. For a long discussion, see https://en.wikipedia.org/wiki/Bitching_Betty

Here are the two studies that are quoted by most of the articles on this topic.

The first is Does social desirability bias favor humans? Explicit–implicit evaluations of synthesized speech support a new HCI model of impression management[0]. This study found that both men and women interpret female voices as warmer.

The second is Are Computers Gender-Neutral? Gender Stereotypic Responses to Computers[1]. This study found that male voices are preferred when discussing computers and female voices are preferred when discussing relationships.

[0] http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.669...

[1] http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.536...

The warning voice in the B-58 hustler was made female because studies found fighter pilots pay more attention to female voices under stressful situations. There is an obvious "lol" reason for this, but the reality might just be the human ear can hear female pitched voices better when there are distracting noises. Deep voices are often difficult to hear.

Sexism: Siri's secretary-like, menial role is still marketed with a woman's voice.