That is all depends. Have to ask yourself is
(1) Is it been develop by solo or team/company? How experience they are? (writing, grammar, graphic/animation designing, etc)
(2) Is it is a part time or full time project?
(3) Is it simple or complex story? Is the story completed? Do they have the flow chart ready or not? If no flow chart, do they have project planning chart?
(4) Does it have funding to support the project?
(5) Are they working on multiple VN project?
I know certain number of developers do it on their own spare time, Patreon may not be enough to support them to focus on it as a full time. Keep in mind the amount they get per month (depending on the requirements to earn it) there are Patreon fees, then taxes and etc. So they do not get that amount you see posted on their site. Since COVID-19 hit world wide, it had effected a number of developers as well users. We all just need to be patience for the next update. If you are not pleased, there are other VNs to explore while waiting for the update or move away from the VN's forum that you are not pleased.
Have a great day and be safe...