Or it's just a sign that ND made her completely irrelevant to the story, and to a lesser degree, made Sarah irrelevant as well. She only existed to build Joel's character background. The story was about Joel and Ellie.
Also, it's impossible for you to say absolutely zero people have ever wondered or talked about the mother.
http://www.gamefaqs.com/boards/652686-the-last-of-us/66507912 Here are people talking about the mother.
http://community.us.playstation.com/t5/The-Last-of-Us-General/Spoiler-Tess-was-Sarah-s-mom-Joel-s-daughter/td-p/41212325 More people speculating about the mother.
I'm sure I could find a lot more if I bothered. People have pondered the identity of the mother and why she and Joel split. It's not a big deal in LoU discussions simply because it was irrelevant in the story.







