Due to lack of developers, reimplementing the Win32 subsystem proved to be a much too complex task, holding the project back. Given the deficiencies of the current implementation, developer Aleksey Bragin decided to rewrite it from scratch, drawing heavily from the Wine project.
Bragin's announcement on the ReactOS mailing list makes a compelling argument for this decision. Here is to hoping this will boost development for both projects.
Link to Original Source