I missed the fact the only place you had GUI was in the subject line. I do know what a GUI is.
As spbogie says, it's been mentioned several times, none of the team have found time to do it the way we truly dream it done.
Most of us devs prefer the autocomplete we wrote into ulx over point and click.
Start typing 'ul' in console, Gmod places a drop down 'ulx'.
Hit space, start typing "add", ULX places dropdown 'adduser, addgroup', you can use arrows to select, then start typing name.. etc etc etc
Many of the server hosts we know don't even use the Gmod game client to administer, they use HLSW or a control panel.
This is why GUI has never been a primary focus. Console usability has.
Ahref, he wants a user manager for the menu, rather than console commands.