I have been sort of grappling with this feeling myself. On one hand, it's presumably one person developing, and I really don't want to dump too hard on somebody creating anything; good on them for even trying, much less following through. On the other hand, I don't think I've ever played something where I got the distinct impression the creator got bored of it half-way through like this, and I was so looking forward to this release that it releasing the way it did was a huge bummer and I've still got feelings about it lol.
My guess is that the beta got a ton of unexpected positive reception (especially on youtube), and it created a situation where the dev probably felt like they were leaving money on the table by not developing further, even if they lost interest. Also, honestly, I think the "wander around liminal spaces" as a main concept to develop around makes a much better brief demo/vertical slice than a whole game. Most crucially though, it's my fault for hyping myself up into thinking an indie Unity project was going to approach double-A levels of polish. An idea the v2 beta did put in my head in all fairness - I really thought it was that well made.
Whatever actually happened, I also don't expect to see much more activity on this project, even if I'd like to be wrong and see it make a huge turn around.