Some of the slowness is a result of the quality that makes this game so special. Most games give you too many soulless, empty locations with nothing to do or interact with, minimal flavor text, and few or no background characters. Basically meet and fuck your harem in a sterile setting that feels like cheap window dressing.
This one is more about making every location have stuff to do, making side characters worth interacting with, and generally making a more engaging experience. I expect the story and variety of scenes will speed up as more locations and side characters get finished, since each update seems to be slowed by the time it takes to draw all this. But a library of art that can be reused without sacrificing what makes it special is slowly building up.
This is one of a handful of porn games that has real creative vision behind it. It can take as long as it needs.