Because the prologue of the game is complete.
Besides they not on Patreon anymore because of not being able to make content they wanted to make for the game, and that patreon claimed that they were making games with incest or loli and flagged them every time, while the creator themself already countless times said to them, that there is no incest or loli in it. So they left Patreon.
Discord is the likely only place for you to try keep up with news on a new sequel to the game, maybe.
Screw Patreon and its content restictions. Its like going to a church and be pitchforked if you try make adult content that resemble things they dont like on Patreon.
Viewing post in Monster Girl Island: Prologue comments
It does not have Loli (Children/ young-like used in porn or romance). They just kept flagging them that they did, without even understanding what they were making in the game. Like understand this, if you made a game that has dwarfs in the game, would you not say they are not a Loli? No of course not, but they would still flagg it for it being Loli, because of them being small.
Fun fact, you can be put up as a pedo for having a relasionship with an adut person that has dwarfism.
Payment methods from that site does not support all types of payment, so they didnt want to take the chance with them. Plus alot of the people supporting them didnt just use normal payment methods, so they would lose alot of members for it. So instead of trying to switch to a new one, they decided to just leave Patreon and stop getting funded for the game developments. Now they will try do it when they got the time. And for free.