Additional anecdata, and also a woman:

I do this for any or all of the following reasons:

* (culture) it is polite to leave something for the next person

* (I have roommates) I don't want to be the last person who finished something. I would be obliged to replace it.

For the typical girl thing, I haven't seen this behavior in real life with my family members or friends. I have heard of the concept on social media.