I’m sorry you feel this way, however the explanation is actually a simple one 
Firstly, fingerprint unlock is the preferred app unlock method of choice for the vast majority of users. The amount of requests we get for an alternate solution on iOS, where we’ve had TouchID unlocking for a long time, is tiny.
This is not unique to our app, many apps that have fingerprint based authentication don’t have alternative options.
Secondly, fingerprint unlock on Android is entirely client-based, whereas implementing a PIN method requires significant work on our back end, too. That obviously makes it a larger project requiring more resources.
That doesn’t mean we won’t do it - it’s just that we’ve not scoped it out yet and we’d like to look at the data we get from shipping fingerprint unlock first - if 99% of compatible Android devices choose to use the feature, it’s clearly a less pressing issue than if barely anybody elects to use it.
Fingerprint unlock, as it’s coming, is something that will be helpful to many users. It won’t be the perfect solution for every single person, but like everything will iterate and improve over time