Re Sam Larner quote
"serious singing was among your mates who liked the songs, usually at home or at sea"

So, that's what happened before folk clubs existed. At sea, on the berry fields, in the factories, mines etc and in the community too. Also, people passing songs and tunes to their children who would share them with each other in street games etc.
There was also the more formal music hall tradition too and people getting together for "a song". By their own accounts, when the early collectors were doing their field work, many of the source singers also had many "modern" songs of the time in their repertoire too. They didn't think of their old songs as "folk" or "traditional" but just songs.

Of course, much of the above was almost lost in the modern world and folk clubs and the work done by many performers, activists, academics and so on in preserving same and keeping the music alive was very important. I don't think anyone is disputing that.

However, as Dave says, there are other ways. Many are fairly similar to or adapted from the folk club model, of course, but some will be quite different. Not all changes will be for the good, I'm sure, but that's always been the case.