Not one of those had free drivers on any consumer-available hardware, so you're limited to kernels compatible with your binary blobs, which then limits your userspace, which leaves you firmly stuck in the insecure, slowly bitrotting past. All of them except Tizen were using Android kernels and bionic libc, and Tizen is a fucking garbage fire (read some of their GPL dumps or try to navigate their bizarre code-dumps-in-branches repo structure sometime).

Desktop Linux is a success (as in, a viable option for those who want to avoid the downsides of proprietary OSes); the only reason there isn't such a viable non-user-hostile OS option on phones is driver support, and this effort says they'll ensure free-software drivers.

Plus, by avoiding the braindead "App Store" model, you instantly have access to a huge and growing base of software, all for free. Finding software for Android is a hellish experience marred by invasive ads, malware, loads upon loads of spam, crappy wrappers for actual free software, profit-grubbing clones on the app you actually wanted, etc. By removing the perverse incentive of "users = $$$" the user experience of finding software improves drastically.

The GUI of most free software isn't well-suited to a phone, but I would far rather wait for UI revamps while using software that does everything I want, as opposed to having to just shrug and give up on finding a web browser with a web inspector--what I ended up doing under Android and iOS.