BUT could you explain to me why a Serissa does not make it as a Bonsai in
the Traditional world ?

On the contrary, although the Japanese traditionalists don't use Serissa much,
you see it used frequently in Chinese penjing. Some of the purists don't
approve of serissa because in nature, it is not really a tree, but a small
shrub. However, I think the real reason is that it is very finicky & not very
long lived. Serious artists want to put their effort into plants they can
bequeath to their grandchildren. I love Serissas, but they don't like me.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)