Working on a game myself, I can tell you that it's way more time consuming than I thought it'd be. Especially posing, getting the lighting right, actually writing a coherent story, coding story branches, etc. A good computer helps with rendering times but the vast majority of time is spent on non-rendering duties.
Especially with a sandbox type game where there are multiple decisions and multiple paths. The add animations to the whole thing and you just tripled your workload.
This whole thing has really made me respect the devs that put out small but consistent updates and stick to their schedule. I'm not making excuses, but the work that goes into making these is a lot more than I think most people think it is.
But yes, adding more and more girls really expands the breadth of the game and creates a workflow problem. Not only do you now have to render all these girls,get their poses, set up their animations, but you also need to place them in the story in a good way, or be lazy and just say they're a slut at the expense of a good story.
Basically, there are a lot of small moving parts where one small brouhaha can cause a chain reaction of delays.
all that you said is true, however there is 1 question remaining, how many people are working on the project?
you see when you start out for 1 or 2 people this is without a doubt a time comsuming project and most likely will not have the supp from backers to do it alone, so you have to have a full day job to also support yourself
however, this is not the case for many devs that have already " made it " (from a somewhat sustanable income point of view), as of this moment they sit at around 3050 backers with tiers ranging from 1$ all the way up to 40$, ofc i imagine that most of the people are sitting at 1$, however, in order to be able to get the game you got to go at least up to 10$ / month, so i would say that it's not entyrly out of the question that they make ~ 15 k - 18 k / month ( before patreon takes its share )
why did i bring this up ? simple, with this income this is the point WHERE A RISPONSIBLE DEV invests some of it back into the project on things such as extra rigs to speed up the rendering speed or, MORE IMPORTANTLY IN MY OPINION, hire new people for the time consuming tasks witch don't necesarly involve rendering, because like you mentioned there is a lot of work do be done witch is very time consuming, but does not necesarly involve rendering.
trust me people understand that everything is not so easy as it is at first glance, but you can't say to them that after a segnificant financial boost, the project will not only slow down but also might take more time than before, AND sometimes have even less content than before. they are not stupid they know that something is fishy there and that there $$ supp is not spent wisely
*note what project are you taking btw, is it something already released or still in early dev? or is it something not aaaam f95 material?