To cut right through it, I think the label reluctance to fully embrace downloadable lossless Atmos comes down to good old fashioned piracy concerns. IAA is DRM free - as it should be and a prerequisite personally for me to purchase any digital media. The Pineapple Thief has a loyal fan base that will buy their stuff, but if Pink Floyd for instance put their catalog up for lossless Atmos downloading, 1. they couldn't gate-keep the Atmos mix by forcing you to buy a $150+ limited box set (Steven Wilson - looking at you too) and 2. obviously it would be pirated to hell, and the group of people who are technically savvy enough play back via Kodi or whatever are also technically savvy enough to "find" it.All three major labels sell downloads through platforms such as HDTracks and Qobuz using a similar business model, so the legality is clearly not an issue. Yes, labels are protective of their IP and there are digital distribution agreements to navigate - but my advice is to pay attention to this space over the coming years, what you see may surprise you.
With traditional 2 channel streaming, the music industry has obviously figured out that people will pay a reasonable amount to have access to any song ever commercially released in 10 seconds, in lieu of pirating. I think the labels are just afraid of losing that control again.