Lonnie's influence was so enormous was because people loved him. That may be difficult(or impossible) to explain to younger people now, who weren't around in 1956. But his Rock Island, Lost John etc aroused very powerful emotions in people: the combination of the power of traditional folk song with Lonnie's extraordinary charisma was unstoppable.(It goes without saying that no performer of traditional song in Britain has had anywhere near that popular impact since, alas). John Peel famously was scarcely able to speak on the radio for the tears when he was announcing Lonnie's death and playing a few tracks on Radio 1. I heard the news of the death announced on Radio2 when driving up the M6, pulled in at the next service station and sobbed and sobbed.
And yes, My Old Man's a Dustman was shite. But quality shite.