"I suspect a lot of it was simply because MacColl was a Communist"
It was Alan Lomax's suggestion that singers in Britain looked to their own national repertoire for their source material.
When he first came to Britain all the singers he met were singing a hodge-podge of songs from all over the world, America, Africa, China, Russia, Germany, Israel... you name it, they sang it; Ewan and Bert were singing American songs; there's a recording of MacColl singing Sixteen Tons for a National Coal Board film somewhere here.
The WMA (Workers Music Association), the fore-runner of Topic even released records of it by The Clarion Singers, Paul Robeson, etc. - used to have some of them at one time.
The hand-over-ear technique is a centuries-old technique, used internationally - we have a photograph of Bengalese temple singers using it somewhere, and the Bengalese singer/teacher, Kali Das Gupta, who lived in London in the late sixties used it all the time. Leslie Shepherd used a woodcut of a nineteenth century broadside seller likewise in one of his books (I think The Broadside Ballad.
One of our Irish Traveller singers described his father singing in the pub with his back to the crowd and his hand cupped over his ear some time in the 30s/40s "just like that feller Ewan MacColl".
Lloyd said it was popular with Eastern European singers and it is a toss-up whether it was he or MacColl introduced it to the revival (MacColl devised various vocal/stage techniques for his work with Theatre Wokshop, relaxation, voice production, projection etc.)
I seem to remember that The Watersons sang with both hands cupped over their ears on occasion.
Jim Carroll