That likely would have messed up hotkeys that people have made for switching what they have set based on the current situation.
They may have done something like that in the past but that doesn't mean that they will always do it. Once you learn the new numbers it should be easy enough to change as needed.
/show 3 is just first, last, and guild names which doesn't include titles and suffixes and /show 4 is everything.
The new functionality was added as option "7" because "4" already had established functionality and many players would have this in their .ini files. Them logging in to have a different name showing and forcing them to change felt bad. I've also found it's best not to add new things in the middle of a list from previous experiences. For reference, these are the current options for the /shownames command. Anything other than these (such as "all") will default to option 4 and show everything. /shownames 1 - First names only. /shownames 2 - First and last names. /shownames 3 - First, last, and guild names. /shownames 4 - Everything. /shownames 5 - Title and first names. /shownames 6 - Title, first, and last names. (New!) /shownames 7 - First and guild names. /shownames off - No names show.