Probably the sublicense wording that many techies confuse with relicensing.
Also sloppy wording in discussions like HN where "relicense" is sometimes used as a shortcut for "combined with a compatibly-licensed work in a larger work that can be used under the whole-work license".
The MIT license is not very long, and it contains this sentence:
> The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
Which clearly state that you can't remove that license to put your own.