In reply to felt:
In the comments in my link it's stressed that the beat plane of shorter conductors is lower, so higher-desk violinists and cellists, and other players near the podium don't have to strain their necks to such an extent to see the baton. This suggests that shorter conductors might have more control over an orchestra.
I wonder if this predominance of short conductors reflects something of a Napoleon complex among them. In Dad's Army, Mainwaring would undoubtedly have taken the baton, while of the tall men I can see Wilson as a violinist, Pike on clarinet, Hodges on tuba and Walker touting tickets outside.