The Trad organisation of which Jack speaks doesn't, in my opinion, really prepare its students for life in the real traditional music world.

There is also the expectation and a sense of entitlement which many of those who attend the courses seem to have in that they have a right to play, perform, and enter any session or singaround they choose.
Of course, they should be always made welcome within reason but the "old hands" can't be blamed for being a little wary sometimes.

So, often, these "new" musicians will just organise their own arrangements which are sometimes quite far removed from what one would have expected from a traditional style session.... This might be playing tunes from books, singing from song sheets, or groups of 30+ musicians playing the same session standards "ad nauseum".