Well it was going to be a 2 chapter game because they said if i remember well that ch2 will be the last and no ch 3.We have been told that the current chapter (i.e., the third) will be the last of for this particular game.
For awhile earlier this year, we thought there might be only two chapters - then they revealed this happy surprise to their fans (and there was much rejoicing).
But due to some things like the game Melody is coming to an end, that lots of routes in DMD like Jennifer were almost not implemented (i mean there is almost no content in lots of hours in game and the relationship with some character are not even began).
I think its because now they have to make a game in substitution of Melody and if they finish DMD too they will have to make another game too.
In addition as i said earlier DMD has lots of things to do unless this was not planned at this point so they decided to make a new chapter so you can download it without memory problems and add some things to bring more surprises to the game like D fooling around, what seems to bring back the corruption tag they removed time ago.