A few things off the top of my head that will make cold starting more difficult than it needs to be, aside from what's already been mentioned:
Poor connection between plug wire and cap.
Crappy, old plug caps or wires.
Old, dirty spark plugs..
Improper timing and/or points gap settings.
Improper valve clearance.
Imbalanced or partially clogged carbs/carb vacuum leak.
Carbon build-up in combustion chamber.
These are basically in order of ease of maintenance, with de-coking the combustion chamber being the most labor-intensive but also probably the most beneficial task overall.
It is possible for these bikes to start easily in cold weather. Last week I started my '71 750K at -5 deg F, after sitting unused for three days, with just three kicks of the lever.
Turned idle screw up 1.5 turns
Closed choke fully
Kicked it twice with ignition off to prime cylinders
Kicked once with ignition on, and it started.
It's a combination of having the fuel and ignition systems in good condition, and knowing your bike and what it needs under certain circumstances.