Likewise, if I tried to develop a Qur'an app, it might not work so well, because I have no idea how a Muslim uses the Qur'an. Of course, I could go talk to a bunch and write an ok version, but I'm sure it wouldn't be as good as an app that a Muslim would write (given a developer of equivalent skills).
Unfortunately, that is not really a meaningful thing to say as a guide to behavior: it's like suggesting that someone sell non-apples - meaningful, not wrong, and useless advice. You need to know what demographics developers aren't before that can be useful; you need to know, say, that developers tend to be male, white/Asian, First Worlders, before you can say 'ah, females may be underserved!'
And you need to think of the categories in the first place, like this religion example shows. If someone asks you if developers might tend to not be fans of religion than the general population, it might seem obvious, but 'being atheists' is not the most salient feature of developers.
Developers should become part of other demographics, so they start to feel other people's itches. Understanding the itch is the best way to create the right product.
When you pitch a product idea to someone many will come back with "but who would buy that?" when it turns out, there's TONS of stuff me, you, and my mom would never buy... that literally thousands of other people would.