Trouble is, UK (and France and Germany also) have such a lot of fields that the available 26x26 codes scarcely suffice. France introduced numbered codes like LF5922 for its smaller fields, and Germany found ETxx becoming available, reserving those for military fields. But Germany and the UK have lots of fields with no code at all.
Smaller countries like my own have so few aerodromes that more or less logical codes can and do get assigned. Even then, to understand my own EBZH code one must realise it refers to the village of Zonhoven...