What factors influence how easy it is to track-stand a bike?
The interplay between Head Angle and fork rake and trail are biggest factors influencing (low speed/no speed) bicycle handling.    Steep head angles and shallow trail values result in an increased sensitivity (more Twitchy) feels to steering input.

I would argue that these factors are factors that describe the handling responsiveness of a bike and not its track standing ability.... as what works for one person in a track stand may not be the preference of another.... 

Secondary contributors are bottom bracket height which will affect center of gravity, wheelbase length and chain stay length which effect stability.

Learning about these frame attributes and what works for you in which situation will not only help you identify what enables your track stand but also help in making informed frame selections by looking at spec sheets.

Finally, looking at your list, if I where to generalize without knowing the detailed specs... it seems you can track stand on bikes with shallow head angles with longer wheel bases/chain stay lengths.