The post by Le20 up above this comment basically explains the reason why.
The artists for Banana Ranch and Baradise Escape are different. For Banana Ranch, my only workload from now on is writing the scenes then coding in the CGs once they're done. I'm in the phase of waiting for the CGs to be completed (for Finn's route), so rather than idling around while waiting for the CGs to be completed, it is much better for me to work on another game. It is in fact very common for a small developer to work on multiple projects at once. Yes, sometimes more than two at once. Yes, sometimes those projects end up being scrapped before the public knows their existence to begin with.
Each route has more than 20 unique CGs (not including variants), which takes a long time to draw. I don't want to cut corners for any route, so it will understandably take time to finish. Making game takes a long time. If you have pre-ordered the game and do not want to wait, feel free to request refund. I'll happily process them.