Why does Apple continue to do some things so badly - the latest IOS9 Mail delete all option is not thought through?

In IOS 9 Mail, Apple has added a Delete All option to the individual email accounts but failed to allow selection of mail you might not want to delete. The Mark All button should allow all emails to be selected and then allow the user to deselect individual emails that it may be desired to keep and then allow deletion of all remaining emails. Why can't they do this? For a company that is supposed to be so tuned in and smart they really do do some things in an appalling way.