Shed Farming actually was discovered way back in early 2019. However, it was pointless to waste all that cash on disruptors and fences as the farming methods at the time were effective and cheap. The shed windows were also hard to shoot through with bullets as zombies spawned not in direct view of the window. No zombie was threatening enough to combat farmers before being shredded by a bunch of P90 and RPG shots on other maps.
When the Champion was added, all forms of farming, even void, were obsolete as the Champion could tank all the shots. Even if they could take out the Skull Champion eventually, it would most likely kill many survivors destroying party share for all of the parties that had a member die from the Skull Champion. Other zombies were able to attack now since they weren't being spawned camped anymore and could assist the Champion in attacking the survivors. It even made void farming obsolete as the Champion could guard the four ammo stations and allow the other zombies to kill the survivors since they don't have any ammo. People soon tried to find other farming methods and eventually found out that if the Skull Champion spawned inside the Stud Harvest II shed, it couldn't get out. If disruptors were placed around this section and a fence was planted, all zombies including champion would spawn in the shed and could not escape.
There was still a problem. It was hard to shoot bullets through the windows to hit the zombies. However, explosives could be shot through the window and kill the zombies! what explosive should we use? Explosive ammo was non-reloadable and the RPG chewed through ammo stations too quick and was inconsistent, the M202 and Xmas Launcher were too weak. But the Chinalake was fast firing, reloaded all grenades with one ammo station reload, and dealt 500 damage per shot; one-shotting all zombies besides the Brute and Champion. You also got more shells when you equipped the Flakvest.
There was even more of a reason to do this on the shed in Stud Harvest II. You see, if you placed a truck or some other obstacle over a spawn to prevent zombies from moving, the Champion is very big and can occasionally spawn on top of the things that were placed to prevent movement. Well, on the shed in Stud Harvest II, you could place towers and fences on top of it. The champion spawns on top of the shed and gets stuck since it is blocked off by the all the fences and towers placed on top of the shed.