The problem is that stuff like privacy and open source don't attract the vast sums of venture capital that ad-selling businesses do. Sure, an average dev could probably build a working app like that - but could you ship the same quality as someone who can afford to hire an entire UX team?
imo, the real problem is that you need to consistently ship. It you made a one-off app then it's going to get de-listed for not being updated despite not needing an update.
With how fast OS changes happen these day and features get added or deprecated, an app not needing updates no longer exists. Even if you design something for iOS 18 or Android 16 today, there's a very high chance it won't even run on modern phones anymore in a few years.
Seems too nerdy for the market at large - the correlation etc. features might well be as good as or better than what the likes of Flo provide, but people will have a harder time understanding that than simply 'your next date is expected to be x', 'your cycle is typically x days', etc.
We definitely cater to a niche that wants to know the nitty gritty details. We’re trying to layer the app such that you get the TLDR first if you want, and can zoom into the details of why second
Maybe you would like to contribute?