Because there's no point to reimport them.
Send them to your lab and delete the exports.
You could use the ExifMeta plugin to view the ICC profile in LR.
There is a point to reimport them.
I use LR as a DAM
and if a client wants me to send him the exact same copy of the image,
I cannot rely entirely on LR to do that (see what's happening with point curves).
That's why I want to keep the original files (same process version/identity plate).
I play safe...
Besides, this was just an example of the necessity of knowing the file profile.
I still have no answer to my question.
LR displays extensively all Exif/Iptc/etc data, but not the ICC profile !!!
PS : J.R. Ellis - thanks for the ExifMeta suggestion.