If we assume we all fly well (either direction), and we all understand
the importance of controlling airspeed during landing, why is the
number one pilot error that is causing injury the stall/spin while
turning to land?

Get away from the idea that you can stall all you want safely at
height, while down low, you no longer have that luxury. Get away from
the idea we all are responsible for flying the plane at all times.
The basic fact is we are all trained and should be able to land
safely.....yet, repeatedly, the same errors are being made by stalling
during the landing pattern.

Is it pilot distraction that creates a laspes in monitoring airspeed?
Or is it habit?

With any physical activity, people develop habits thru repetion. Turn
right 100 times slowly, then turn right fast...it will feel different.
Will you instinctively slow down the fast turn to match the previous
100 slow turns? I think that is very possible.

Here is a way to check your habits. Next booming day, try 10-20 turns
to right at say 40 knots, then speed up to 65 knots. Can you hold 65
knots in a right turn now? Likely, but I bet you glance at the
airspeed a little more than you did in the previous 10-20 turns.

It just seems logical to me if you spend several hours flying slow,
you will tend to continue flying slow unless you specifically make
yourself fly faster. Get distracted, and you will go right back to
flying slow. Talking habits, here.

Is this habit of flying slow contributing to the stall/spin problem
when landing?