Maybe it helps people to understand the current situation if I try to explain my view of the K-9 Mail project.
I work on K-9 Mail because it’s the app I want to use. Having the app work for me is my primary goal. I imagine it’s the same for everyone else who has ever contributed to the project.
Like many other open source projects we package the app and make it available to the world. There is a bit of hope that this will attract new contributors, who in turn will help to make the app even better. But mostly it’s done because it doesn’t cost us anything. If the app works for us, it will probably work for others, too.
Sometimes I implement features that people ask for, but that I don’t use myself. In part that’s because I like technical challenges. But helping others also feels good.
I can’t speak to the motivation of other contributors. But I imagine I’m not unique in this regard.
Having a lot of users or good ratings in the Play Store is not something that is important to me. Sure, it kind of feels nice to know that a lot of people use something you have worked on. And the large number of users that find the app valuable is what brings in enough donations so I can dedicate a significant amount of my time to K-9 Mail. But being “successful” was never a goal. Creating the app I want to use is my main motivation.
With that in mind, most of the answers to the questions that have been asked should be obvious.
Why did you remove/change X?
Because it’s not important for my email workflow. And probably not to that of any other developer who contributed to K-9 Mail in the past 2 years (that’s how long the UI is roughly in the state that it is in now).
Some features are cheap to maintain, some expensive. When something requires a lot of work, but nobody is around to put in the effort, it’s often easier to just remove a feature.
I don’t feel like I owe users of the app anything. Most of the time I do enjoy helping users, or implementing features I don’t use myself. But K-9 Mail is not a product. There are no customers. We create the app we want to use. And if you like using the result, that’s great. If you don’t, that’s fine, too.
K-9 Mail is an open source project. If you don’t like the direction the app is going, you can always fork it, or, assuming most of you aren’t developers, pay someone else to modify K-9 Mail’s source code to create the app that you want. I think that’s quite a great deal for a free app (that doesn’t track or otherwise monetize its users).
EDIT: You might want to read the follow-up here.