They've been around since CB radio was carved from the Amateur Service.
I once saw an old man fight in a supermarket lot over who snagged the most dx back in the call letter days. "Fight" may be an oxymoron for what occurred. They put 'em up, one guy bum rushed the other, ran into the guy's forearm, and hit the pavement. The "winner" got in his truck and drove off.
Our defeated CB warrior got a ride to the hospital in the funeral parlor ambulance. They took you to the hospital and hauled you back to the funeral parlor for a nominal fee if you died. Our brave warrior lived to fight another day.
Awesome.
Pigmeat is right - the original 26.96 MHz - 27.26 MHz allocation was taken from the 11 meter amateur band...and that became the original 23 channel Class D CB service. 27.235 MHz and 27.245 MHz (as well as other frequencies in the 27.4 MHz - 27.9 MHz region) were allocated to business users, 27.255 MHz being shared with paging and telemetry as CB channel 23 (it still is). When they went to 40 channels in 1977 they added 27.235 MHz as channel 24, 27.245 MHz as channel 25, then 27.265 MHz as channel 26 up to 27.405 MHz as channel 40.
27.430 MHz, 27.450 MHz, 27.470 MHz, 27.490 MHz, 27.510 MHz and 27.530 MHz are still allocated to land mobile radio...and yes, there are a few systems still using those frequencies (nearly all of them using 27.43 MHz, 27.45 MHz, 27.47 MHz or 27.49 MHz - 27.51 MHz/27.53 MHz are allowed CB power levels only).
Of course, the 25-28 MHz region is peppered with freebanders, hunting clubs, DXers, Latin American taxicab companies, fishing boats, truckers using their “company channel” etc etc