Regarding “other use cases”… many folks with tablets tend to put them in a stand in landscape orientation and utilize them while in the stand. For iPad, it is often the case that switching to portrait means removing the tablet from the stand and also having to remove the power cable. This, IMO, is a much more frequent use case than disability/accessibility.
Further, Apple’s developer guidelines state:
If possible, support both portrait and landscapeorientations. People prefer to use apps in different orientations, so it’s best when you can fulfill that expectation.*