Canonical maintained them anyway, though, just not officially. Sources: https://lwn.net/Articles/618862/ https://lwn.net/Articles/667925/ https://lkml.org/lkml/2015/12/15/538. I don't see more recent announcements; I don't know if they stopped because of continuous rejection of their community contributions from upstream, or if they are continuing anyway and I'm not aware.
Disclosure: I work for Canonical. I'm not authorised to speak for Canonical, expressed opinions here are my own. [Edit: I should add that I don't work on the kernel so I feel like I'm as much an outside observer as you probably are]. But I'm not sure I'm even expressing an opinion here - just citing some relevant, publicly verifiable facts.