Chain-of-command portraits serve a practical, if minor, function; yes, more of them change when a chief executive changes than anyone else, but they also change when a batallion commander or civilian agency director changes, for the same reason as for a chief executive.
Heraldry of the monarch also serve a function, I suppose, but it is less like a chain of command photograph and more like the US national coat of arms (or the Great Seal, which has the former on the obverse); neither of which has changed substantially (there have been some rendering tweaks) since adopted by the Congress under the Articles of Confederation in 1782.
And that function is that (for example) on a big Navy ship with thousands of sailors, the "lower ranks" might never have laid eyes on the commanding officer ("CO") or executive officer ("XO") but need to recognize him/her if s/he shows up unannounced and alone in a workspace — following the old nuclear-Navy rule that "you get what you INspect, not what you EXpect."