Yeah, I've seen the sales figures. However, I would say that quite a lot of the anime that is released has limited crossover potential. By which I mean, it will sell only within the 'anime fan' demographic that has already been carved out but doesn't have as much appeal to general cinephiles (for lack of better terminology - I don't mean to be condescending or insinuate that anime fans like the good folks on here don't love film). The 'old and obscure' stuff may well do, though it is natural that distributors are hesitant about taking a gamble on, well, old and obscure stuff.
I'll readily admit that I'm no Nostradamus when it comes to predicting how a title will sell - it's difficult when its a film that has never been released before and there's many unknown variables (marketing, coverage etc.). But I think Angel's Egg has potential, especially if pitched to the arthouse/cinephile crowd. That's certainly a demographic that would also be interested in the hypothetical release of Momotaro's Divine Sea Warriors. And while you may ask why not leave it up to Masters of Cinema or Arrow to release, animation isn't their forte (MoC have released some Rene Laloux but that's it) and, from what I've read, anime licensors are generally not the easiest companies to deal with so it might be better if left to someone used to dealing with them.
Ultimately though, this is all just conjecture on my part - Andrew knows best! I'm just giving my 2 cents as I'd love to see it released!
For a film I'd quite like to have a release of but will admit has no sales potential whatsoever, take a look at Nagisa Oshima's only "anime" - Band of Ninja!