"Anais has been very open that when they went to edit and mix the performances, they realized they needed more time to finish it at a level where it was exactly what they wanted. So, the complete thing isn't ready. This isn't a strategy. They probably thought releasing something would be better than holding the whole thing back, but nevertheless, the Internet persisted."
I'm sure haterobics is right. Of course they wanted the album out on June 7, but clearly things didn't work out that way. If Hadestown indeed wins the Best Musical Tony on Sunday, they would want the album available just as the show is getting all that award-winner exposure. I suppose they figured some streaming service presence is better than none at all. It's not ideal, but it seems understandable.
That said, the Spotify situation is a bit frustrating. When I searched "Hadestown,' the only Broadway track that came up was "Way Down Hadestown." "Our Lady" is under Amber Gray, and "Wait for Me" comes up under Andre de Shields. It doesn't link them into the same album--indeed, the "Wait for Me" intro doesn't even come up as part of the same album as the song itself. I'm sure this will all be fixed once the full album comes out, but in the meantime, it's a little laborious. Not a deal-breaker, but a bit clunky. THAT said, the recording sounds great!