Like you said, they were a fad for most people that died out well before mobile phones became popular. Even REACT, a group that used channel 9 to help people out seems like it’s all but dead, and I have heard a lot of non-emergency traffic on channel 9. CBs are still sold and in use, but mostly by truck-drivers. There are still some people who have base and/or mobile stations and talk to each other locally and over longer distances by ionospheric skip. As far as local communication goes, they’re pretty useless. I have one that I hooked up to an antenna I use for cross-country as well as local communication; it didn’t do too well, and it didn’t do too well on a vertical antenna 20ft off the ground.
Disclaimer: I spend most of my time on amateur radio bands, so I am not that much in touch with the CB world. This is my impression from infrequent use of my CB in my car and research on the web. I invite corrections and updates.