JK_Dave
Caught the Bug
Thanks to Wikipedia, this might answer that question (slightly edited):
America
21st-century use CB has lost much of its original appeal due to development of mobile phones, the internet and the Family Radio Service. Changing radio propagation for long-distance communications due to the 11-year sunspot cycle is a factor at these frequencies. In addition, CB may have become a victim of its own popularity; with millions of users on a finite number of frequencies during the mid-to-late 1970s and early 1980s, channels often were noisy and communication difficult. This caused a waning of interest among hobbyists. Business users (such as tow-truck operators, plumbers and electricians) moved to the VHF business-band frequencies. The business band requires an FCC license, and usually results in an assignment to a single frequency. The advantages of fewer users sharing a frequency, greater authorized output power, clarity of FM transmission, lack of interference by distant stations due to "skip" propagation, and consistent communications made the VHF (Very High Frequency) radio an attractive alternative to the overcrowded CB channels.
Australia
Before CB was authorized in Australia, there were hand-held 27-MHz "walkie-talkies" which utilised several frequencies between the present CB channels, such as 27.240 MHz. By the mid-1970s, hobbyists were experimenting with handheld radios and unauthorized American CB radios. At that time in Australia, the 11-meter band was still used by licenced ham operators, but not yet available for CB use. A number of CB clubs had formed by this time which assigned callsigns to members, exchanged QSL cards, and lobbied for the legalization of CB. In 1977, CB was legalized with an 18-channel band plan. In 1980, the American 40-channel band plan was adopted. From the outset, the government attempted to regulate CB radio with licence fees and call-signs, but some years later abandoned this approach.
The first CB club in Australia was the Charlie Brown Touring Car Club (CBTCC), which formed in Morwell, Victoria in 1967 and consisted mainly of four-wheel drive enthusiasts. The club used the prefix GL (for Gippsland), since "CB" could not be used.
With the introduction of UHF CB radios in 1977, many operators used both UHF and HF radios and formed groups to own and operate local FM repeaters. Members of the CBTCC formed what became known as Australian Citizens Radio Movement (ACRM) in the early 1970s; this organization became the voice for legalization of CB radio throughout Australia. After peaking in the 1970s and early 1980s, the use of 27 MHz CB in Australia has fallen dramatically due to the introduction of 477 MHz UHF CB (with FM and repeaters) and the proliferation of cheap, compact handheld UHF transceivers. The Australian government is working on changing the allocation of channels available for UHF CB Radio from 40 to 80, and doubling the number of repeater channels from 8 to 16.
So in short, it seems that CB would have been more popular in Austrailia, but when UHF CB radios were introduced, users had a better signal with UHF and radios were cheap and compact, thus improving their popularity.
