If you download bbPress again and unzip it locally, you can compare the directory structure. Above, I listed the top level directory only, but there are folders with more files in them. I suspect your folders and files did not make it up intact. I would list all the files from my install, but it’s a pretty long list and would be a mess to display. If you download bbPress again just to compare listings, I think you will see the problem.
Basically, it’s the files within the subfolders that are missing (I think).