"Why is it that some tradfolk alternate between sneering at every newbie (whether playing spoons, shakey egg or drum) and then wondering why younger people aren't joining the movement?"

Because the tune is the key and rhythm can only provide . . . well rhythm.

Now I know some fine bodhran players, no spoons players, a good bones player (the shakey egg is a crime against sessions and should be scrambled on sight) and I myself played the drum for many years but at the end of the day you can sit with a tin whistle and make music for people to dance to, but sit with a bodhran or spoons and you'll simply be beating solo.