The post I linked to mentions it explicitly.
"the goal here is to make a better version of C-style containers rather than to implement something C++-style and similar,"?
But a goal is not a reason. I.e. why doing
CONTAINER_OF( user_data, vip );
container_of<&user_data::vip> vip_list;
As to why to do what you wrote I have no idea. These two code snippets are unrelated.
If I were to pick the reason, it'd be simply that I don't like Boost.
To me, Boost is an ultimate embodiment of all that went wrong with C++ when it evolved from being a better version of C into the multi-paradigm monstrosity that it is now. Just look at the man page linked above. How to get a clever little concept of intrusive containers and completely decimate it into a technically correct, but unpalatable formulistic piece of engineering that, above all else, is rid of any shred of elegance that made the original concept so great in the first place.