The Japanese company Key which is known for producing some excellent visual novels, some of which you have likely seen the anime adaptions of like Clannad, released Rewrite two months ago, but according to Push!!, it has only sold just shy of 24,500 copies.
Selling both ero works (Such as One – To the Radiant Season) and non-ero (Clannad, and Rewrite) since 1999, Key has created several visual novels and had multiple releases of their works. Key’s games usually sell around 150,000 copies in Japan according to some sales numbers. To compare this, Fate/Stay Night sold around 147,000 and is considered one of the best-selling visual novels of all time.
The reasons behind this can only be speculated, but with Key’s habit of releasing a title multiple times with expansions, non-ero versions, and in the case of Little Busters, ero versions, the fans could simply be waiting for a better edition to come out to avoid buying the same game multiple times. In Japan, it’s not unusual for this to happen, even though it’s a very alien concept in the US.
A sizable budget went into Rewrite, but its incredibly poor sales could make a deep cut into the funds available for their next title. This is why you can’t make a habit of selling multiple editions of the same game in a rather niche market to where it can get quite ridiculous. It will just end up biting you in the ass at one point and you wont have a budget to make the special edition.
This is similar to what happens with comic books in North America, people will wait for the graphic novel to be released before purchasing it.