Likely a design choice that stems from how humans react to the voices of each gender. Female voices are generally better for voice communications which convey details, information, and other non-commands. Male voices are generally used to communicate from a sense of authority.

Take for instance the NYC subway system. The female voice announces the stop the train has just arrived at, while the male voice instructs customers to 'stand clear of the closing doors' and to 'be aware of pickpockets, take care to ensure the safety of your personal property.'

This is quite intentional. We simply react better when certain types of voices are used to convey certain things.

Source: former audiobook, VO, and podcast casting director.

Siri, at least, gives the option for a male voice. And BWM diid apparently recall their GPS voice system in the 90s because drivers did not want to take direction from a woman:

https://skeptics.stackexchange.com/questions/27244/did-bmw-r....

They are less intimidating and on the whole easier to listen to.

http://www.cnn.com/2011/10/21/tech/innovation/female-compute...

I think it's partially as a result of early science fiction movies having male-voiced robot antagonists. Mostly HAL.

I imagine the skeuomorphism being invoked is that secretaries are stereotypically women.

Siri in UK defaults to a male voice

I'm sorry, but if I hear a male AI voice, I'm thinkin HAL, and that's just how it is.