In two of the later barns (much larger than the crucks shown previous) that I've had the pleasure of dismantling / moving there was evidence of a hay track having been installed. (granted, the hay track came along much later than many of the barns origination dates).

Posting down the center of the barn would have interfered with any operation out the gable ends. These barns had a queen post / purlin roof system - canted if I remember correctly, with posts dropping to the floor below the ties as needed. This kept things open through the upper floor / roof.


Size may not have mattered - here's a pic of me on an oak 'swing beam' on an Ohio barn that was restored into a residence. There were a pair of these and I think they easily hit 12x20 or more in the center (they were tapered from end to middle!). Size was probably easy to come by - but how to get that ridge up in the air might have been a determining factor in not wanting to use large pieces up high...