Maybe they're trying not to get burned by used game sales. Guess they'd have to test out a digital-only title to see what happens.
Being one of the big VN names, I kind of doubt it. Mostly because so many niche VNs get physical releases in Japan.
Not sure how the graphic novel version sold, but the physical anime releases did not do so well. Now I don't think most of the ; anime adaptations minus Steins;Gate sold well but maybe doing the anime before the game this time made them hesitant about physical game copy costs.
This I do see being a possibility. I heard the show itself was... only ok, so that's probably a factor.