Windows was more prominent and didn’t have a real cli culture, Internet Explorer was still king back then. Dedicated Linux servers were expensive, virtual servers didn’t really exist, most people spinning up VPSs today would only have been able to afford shared PHP hosting with no shell access. And most importantly, web development was much simpler back then.
CLI interfaces have none of the inherent benefits you describe.
* They are not inherently completely discovered
* They do not inherently offer more control
* They are not inherently more flexible
In fact, I would argue on all points a GUI interface is inherently FAR superior to a CLI interface in each of these measures. GUIs clearly offer more control and clarity. Ever try to specify a partial list of US states via a CLI?
HOWEVER:
CLIs crush GUIs in my opinion on two CRITICAL dimensions
CLI are scriptable
and more importantly
CLI work over SSH (a rather low threshold to cross)
The ability to productively work in a terminal over SSH is (in my opinion) at the core of the resurgence in popularity of CLIs and other terminal based apps like vim and emacs as well. Yes, chording is productive and even well supported by most gui editors, yet these terminal editors remain super popular I believe in large part thanks to their ubiquity and ability to work over SSH.
Just my two cents and is not an attempt to start a flame war.