H-game development is never usually that fast, just look at Future Fragments and any of Vosmug's games. Hell I remember the laboratory stage in Sinisistar taking a year to release. A lot of these a games are developed by one person or a very small team and often the ambition and scope of these projects lead to inflated development time. If you wanted to be cynical you could say that they are deliberately going at a slower pace so they can farm monthly donations but in reality, game development is hard and time consuming.