I would guess that Glocks are not popular in the UK as the general population can't carry them. When you have a whole lot of people looking to carry guns, affordable, light, durability, reliability etc. are all desirable traits.
I'm not all that familiar with the UK gun laws other than knowing that handguns are heavily restricted etc.
1997 Firearms Act
Following the Dunblane massacre, the government passed the Firearms (Amendment) (No. 2) Act 1997 which means that as of 1997 handguns have been almost completely banned for private ownership, although the official inquiry, known as the Cullen Inquiry, did not go so far as to recommend such action. Exceptions to the ban include muzzle-loading "blackpowder" guns, pistols produced before 1917, pistols of historical interest (such as pistols used in notable crimes, rare prototypes, unusual serial numbers and so on), starting pistols, pistols that are of particular aesthetic interest (such as engraved or jewelled guns) and shot pistols for pest control. Under certain circumstances, individuals may be issued a PPW (Personal Protection Weapon) licence. Even the UK's Olympic shooters fall under this ban; shooters can only train in Northern Ireland, the Channel Islands, the Isle of Man, or abroad.
The act was created in response to the Snowdrop Petition following the Dunblane Massacre. The previous Conservative government had followed the recommendations of the Cullen Report on the massacre and introduced the Firearms (Amendment) Act 1997 that banned "high calibre" handguns, greater than .22 calibre (5.6 mm). This new (No. 2) act further banned the private ownership of all cartridge ammunition handguns, regardless of calibre.
The only handguns still allowed following the ban were:
Taking the above into account, what are you seeing at the range?