The demand for these patches stems from the desire for a more complete experience. Many original doujin games are released rapidly, leaving them open to improvements.
Once a patch is perfected, the community often bundles the game into a "patched .zip" archive to ensure that the work survives long after the original game studios cease operations or stop supporting the software on newer versions of Windows. If you are looking to explore this topic further, ane wa yanmama junyuuzip patched