UK consumers are not the most loyal of people. Many of them rushed out to buy a Vax or broke the trend of buying a particular brand when their last cleaner wore out, in favour of Vax. Vax was a bright, heavily advertised gimmick, and the UK consumer loved them.
Vax also pushed wet carpet cleaning to the front of the consumers mind. Before that, few people seemed all that bothered about cleaning their carpets themselves, and indeed I doubt many who bought 3-in-1 cleaners probably cleaned their carpets with any regularity, even after the purchase was made. Never the less, other manufacturers quickly saw the need to bring out their own versions, with Hoover satisfying their ever-loyal consumer with a machine to rival Vax. I never recall Electrolux making much fuss over their cleaners in the same way as Vax and Hoover did.
We also had some very inexpensive cleaners too, like the Goblin and Moulinex, both of which focused on the budget consumer. Neither was particularly great in quality and performance.