General disinterest in continued development and when it is being developed, its extremely slow and lethargic. Which is unfortunate cause decent Monster Girl games are pretty much non-existent.
Viewing post in Monster Girl Island: Prologue comments
Creator has interest in development of his game - it can be seen through his discord server, where you can ask him directly about it.
If i recall correctly, the cause of slow development is that he is working on the game alone because he wants to make the game by his own vision and in his own pace so he didn't burnout during development like most indie-devs do before dropping their projects.
Quote from his "Leaving Patreon" message:
"As for the fate of MGI, well, nothing about the end product will change. I'll just approach developing more efficiently with less updates and no wip builds"