This should be noted in the front page as that means retail copies are no longer eligible to be redeemed on Steam
Topic on Talk:Borderlands
I saw that information was removed on the page, but 2K said that was the case, should it be put back?
The information was removed as a part of undoing a guest's changes that say the complete removal of the Essential Improvements section.
I've added the information back on the page where relevant, as well as additional information about the upcoming GOTY (2019) version and what it will include.