Glad: Property of GLAD_INCLUDE_DIRS is private

Since I wanted to use glad as subporject of my project, I wrote this code

add_subdirectory(extern/glad) 
...
target_link_libraries(${PROJECT_NAME}
  OpenGL::GL
  glfw
  glad
...

However, GLAD_INCLUDE_DIRS of glad target is set to PRIVATE so that my compiler couldn't find glad/glad.h. After change property from PRIVATE to PUBLIC the problem resolved.

I just wonder why GLAD_INCLUDE_DIRS is set to private
Is there any reason for this?
https://github.com/Dav1dde/glad/blob/ec01ac515dba0730dca375887bb1bd60bc92013c/CMakeLists.txt#L84
To use glad target in other cmake project, I think GLAD_INCLUDE_DIRS should be set to PUBLIC not PRIVATE.