It's supposed to be a time saver. It's a hassle and a waste of time to make a large pillar and then destroy it.
However, /wb also removes the need for finding 4 wood for a recipe that is irreversible. A dirt pillar is cheaper and breakable.
Takes too much space. My inventory is always full to the brim so I cant use that kit. Even if I made one I would throw away all leftovers. And then I will have to go to that place again if I need the workbench. Too. Much. Effort.
-1 Access to WorldEdit commands would not be fruitful as it leads to an infraction on TPS and overall would lag the server if a group of people decided to use it at once for perhaps a speedy building.