Two reasons 
1. /custom_buildpacks/ is not a URI space being used.  /custom_buildpacks/ was renamed to /buildpacks/.
2. More importantly the nginx upload module only supports POST.  When many of the methods were changed from POST to PUT, this path was no longer used.
Some of the other URLs can be removed as well.  If you wish to continue to use the nginx upload module, then you need to get a modified version (not from nginx) which supports both POST and PUT.