It is a feature. Apple determined that it is better for you not to be able to select all. All is too much for the user to handle.
Apple has instead chosen to only allow you to select small amounts of text because ALL is too much. Also, select all allowed some users to select all of an article or other text and this allowed them to save a whole story from a site.
This is not a profitable thing for publishers so Apple decided that the publisher should be taken care of over the user. Apple doesn’t just think that selecting all is bad for you as a user, but also bad for big businesses which are more important than the annoying user.
Thank you for your patronage.
[Edited by Moderator]