What factors influence how easy it is to track-stand a bike? What are the characteristics of a bike that make it easy or hard to track stand on?  



I have tried track standing on multiple different bikes and they are all dramatically different in terms of how easy it is to track stand on them. 


2016 Gravel Bike (somewhere between a cross bike and a touring bike) - It is very easy to track stand
1990s era mountain bike with rigid fork - The bike is a bit small for me and reasonably easy to track stand
1980s era road bike - Hard to track stand on
2010 low-end mountain bike - Hard to track stand on
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.