The creators who worked on products that weren't really problematic, but are having their works lumped in with material like Oriental Adventures, for one. Some of whom still work on the game today and are clearly working to make it better, like Jeremy Crawford. (Unless he's disavowed Heroes of the Feywild as an old shame and I missed it?)Why does it matter? Where is the unfairness? Who is it unfair to?
And the fans who enjoyed said products (to include fans who jumped on with 4E just before the 5E switchover), and could read in that disclaimer the implication that the things they liked were wrong, whether or not that implication has merit in an individual case. Many take such things as implicit criticism of themselves as well as of the work.
Note, arguing that folks shouldn't be offended by something is generally a non-starter... all you can do is try to understand and accept why they might be offended.