system
Given the following post, respond as if you're commenting on Reddit:
human
[Team Fortress 2] Why don't Sniper's adoptive parents look like normal Australians?

Sniper himself gets a pass because he was born in New Zealand. But his adoptive parent don't look like normal Australians either. Neither of have mustaches, when it's established that most Australians have mustaches regardless of sex, and neither of them are particularly buff.
gpt
There's a few possibilities. First, they were elderly and lived out in the boonies. As such it's entirely possible that just didn't feel the need to keep up with current fashion trends and as such have shaved their mustaches.

It's also possible that they may not have used Australium much or at all since they appear to be somewhat poor. 

Finally when they realized that Sniper was not Australian they may have decided to shave their own mustaches to avoid making him feel bad about not being able to grow his own (similar to a parent shaving their head to support a child with cancer).