From the app store numbers, it looks like Wire is still not even to a million monthly active users. For a funded app with a large full time staff and generous marketing budget, that's a pretty terrible sign several years after launching. I know that the founders are rich, but why would they continue funding an app that isn't showing adoption?
Maybe being open source will change that, but I can't see it being a significant factor for the hundreds of millions of users they need to even begin to catch up. I think they were betting on end to end encryption to save them, but their biggest competitor launched better end to end encryption by default before they could.
You're right, they sold Skype twice, so they're not stupid. They're unlikely to keep throwing money away when the writing on the wall is this clear, and word on the street is that they're looking for an exit.