I share your liking for them. My favourite (from the 90s, I think) is 'The Road to St. Ives'.
I suspect part of the issue is that Surman seemed to be (at one stage) deep inside the world of explosive free or near free improvisation. But there are other sides to his musical personality that come out in the solo/duo/choral/strings albums that don't seem to chime with what is considered 'edgy'.
Essential to understanding Surman, I think.
All I hear as personal statements, some with strong connections to his heritage - the aforementioned 'Road to St Ives' and 'Diary of Rev. Absalom Dawe'. I've always heard his more out there recordings (which i love) as the diversion if there is one and the solo/duo/choral/strings to be the thread that runs through