Developers may have their own work schedule and there may be reasons for delays. But why don't they tell their subscribers anything? No one even knows how many images and animations have been made at the moment, there are only incomprehensible percentages.
Probably because that information is completely irrelevant.
Some devs do add details like that to their development updates and at the end of the day it really doesn't affect anything. They're not going to gain subscribers based on the style of their dev logs, they'll gain subscribers if they make a VN that people like.
The status updates only serve as a general progress snapshot to let people know how things are progressing. To let people know how close or far they are to completing the next chapter and the dev can be however detailed as they want about it. So you really don't need to know the exact number of renders and animations completed each status update because all you'd do is nitpick and argue over the numbers. All you really need to know is that
things are progressing.
Besides, render counts in general are completely meaningless. There are so many variables go into how long it takes to complete a single render such as hardware... or the dev's skill, experience, and attention to detail. There was a dude in this thread a while ago trying to shit on Summer Heat's render counts compared to some garbage whoretagonist RPGM game, and I think NPX mentioned at the time that it takes around an hour per render in Summer Heat. Basically, another dev might shit out 4000 renders to Summer Heat's 400, but they won't look even a tenth as good. The only thing that matters is whether you were satisfied with an update, not how many renders it has in it.