I would say if u go on their patron pages there are screenshots of what comes in the game as a teaser and if u really want to see more so go pay for it and enjoy them every month . If people can see all the preview pics and development phase from here for free then they will have no need to pay for the months other than the one when the game releases so that would affect the developer's income. That's the reason they are kept locked only for patrons. Some devs are lenient about it and let it go while some aren't and also this dev is a WOMAN.
I agree to an extent. That's why I mentioned "special" renders. You can have renders you deem for the public, and then you have renders that are behind the paywall. Sometimes, you give the public a gift, a lewd render if you will. For the most part, renders that may provide key information in the plot, or lewds stay behind the pay wall. It's the bait so to speak.
As for monthly subscribers. I have always seen those people as the ones who truly enjoy and want to support the developer in their product. They want the special pictures, they want the interaction with the developer. No matter what you do you are always going to have the subscribers that sub for the for release month and then drop it immediately after they get the product. I might even go as far as to say that there are probably more of the latter type of subscribers.
There is a balancing act that, as a developer, you have to understand that not everyone can afford a monthly subscription for, say $15 a month vs. $5 a month. You need to find a sweet spot that allows you to make a little bit of profit but also maintain as many subscribers as possible while providing value. All the while you also need to be marketing your product. During the time before your releases the way you do that is by releasing pictures and communicating. That's your product between releases.