I agree with you, but in this particular case, it seems to be a free chatting app, not a revenue-making business. From the looks of it, I think the author's motivation for writing and maintaining this are ideological, to provide privacy to users. "This app has no ads, no user behavior tracking and all messages are exchanged directly with the XMPP chat server". Doesn't look like a business to me.

https://itunes.apple.com/us/app/monal-free-xmpp-chat/id31771...