My own theory... I am of the type that conserves my energy, (lazy). haha. This lends itself to not lift my leg and apply the brakes.
also, if you have ever worked on the brakes or braking system on these machines, you will note that the brakes are easy to repair and/or replace, (if you can stand on your head for an extended amount of time). This I only did once, not a pleasent experience.
I would suppose that to avoid working on these, plus being lazy one would tend to not use the break pedals as much.
after you become used to your machine, it becomes like second nature to turn with the control levers, which the book also mentions.
I still use the brakes on mine sometimes if I have to make a pivot turn or am backing up an implement.
And one last thing, because the pedals are both on one side, it is difficult for me to use them independtly. Especally in tight or precarious situations, (hillsides and between utilities).
these are just a few of my thoughts...sl