Because Ruag have indicated that they are not particularly interested in selling reloading components in this country. The same company has however recently revamped their sales operation in the U.S. and are actively promoting reloading using Norma components.
If you look back a few months ago on this forum you will see that we discussed this matter and an extensive list of European manufacturers was given, but the majority of gun shops in the U.K. are aligned with either GMK or Edgar Brothers who both import mainly U.S. reloading components. Therefore the majority of shooters have only seen components that these people supply in their local shops and are either reluctant to try something that they are unfamiliar with or unwilling to start developing new loads all over again.