Can people be encouraged (reminded?) to write a biography once they become regular users? It’s just nice to know something about the questioner and can help you to pitch the answer so it’s at a more appropriate level.
Technically yes, but that can't be a requirement.
We can't really make users complete their bio, or use their actual names as the username, or add a profile bio, or anything of that nature because they have the right to remain anonymous the rest of the community.
The users' only obligation is to provide accurate and complete information when they create the account, and by "obligation" I mean that they are responsible for the private information they share.
Now, users have the right to keep their identity hidden from the rest of the community if they want and a lot of them, especially newcomers, choose to do that.
So we could definitely encourage and recommend a bio update once they become regular members, but that's about all we can do, meaning that we can't make this a requirement.
Even if we were to make it a requirement, people who want to stay anonymous would simply lie, which would get us nowhere fast again. So instead of putting people in a position to lie, we simply give them the option of not completing their bio.
As a side note, once a user becomes a regular member, it's much more likely that they will start to specify their level in the question or in the comments section, so we can always use their feedback to determine the appropriate level at which to pitch the answer.