Maybe I got something wrong, what's behind the term CAS?
Controlled airspace used to be defined as airspace in which an air traffic control service is provided to (and mandatory for) all
IFR flights. Since the alphabetical classification, it is now, by definition, classes A to E (which are the classes that meet the former definition).
To refer to class E airspace as "uncontrolled" is technically incorrect, and may cause confusion in states like the US or Germany where there's a lot of class E at lower levels. The UK has very little class E, hence we've grown quite lax in our terminology.