Because security is only as good as its weakest link, and an adversary who wants your sensitive data won't choose not to break in because your security is "mostly OK".
At the risk of being overly negative, if you have this attitude, you're not building a secure system, and, for your users' sakes, you shouldn't say that you are.
I agree that security should be taken seriously, with care and caution, and that users who ethically need to be aware of potentially fallacious assumptions about the usage of a device should have the capacity to easily find that information.
It's fine if you think this is an unreasonable conclusion to draw based on the evidence; you're entitled to your opinion. But the question is, do you feel comfortable with the possibility of people going to jail or dying because they didn't understand the security tradeoffs that this app makes? I think it's because some of us see this as an extremely real possibility -- particularly given the frankly ineffective security practices described here -- that you're seeing so much backlash.