Wine changes all the Win32 API calls to Linux-compatible calls. You either have to do that translation of calls after-the-fact (like Wine does: it captures those function calls, and translates it), or you have to do it in the original source code (ie, translating the source code to use some method compatible with both Windows and Linux), which would require a complete rewrite, because as @Alan-Kilborn says, NPP is written “from the ground up to only support Windows” – ie, using Win32 API.
It’s not impossible to do; it’s just impossible to do without a complete rewrite (at which point, some would argue it ceases to be Notepad++, even if it is 100% feature-compatible).
