I can explain why - This game started out as a learning game. It wasn't supposed to get this big.
I'm a writer first, then a coder, then an artist. I had no idea how to do replays or anything other than basic Ren'Py when I started out nearly four years ago, and as I never actually use the replay feature when I play games (it really wasn't around much back then), it never became a priority. Hell, going through the comments will show you that I didn't even know about the nipple morph for most of Volume 1.
When I finally finish this game in the next update, the other two games I'm working on will have replays and some other fun things like music, SFX, and a much more customised interface, but to go through and add all that in here would break saves, and I really
really hate to do that.
Finally, my rule on updates is this: They're done when they're done. Trying to fit them in a schedule usually leads to anger and broken promises.