Well past 2008 that was acceptable for ag buildings, and if it was wired that way back then, it is still acceptable now, grandfathered in. So you should pass inspections just fine.
Your troubles start if you want to add on to the wiring now if your county adapts a much newer code - not all places have. You end up needing to go back to your main box now if the local code has changed to the newest code.........
As to why, think about your plumbing.
You have one pipe coming in to your house, the pipes are all joined together at one spot, but one goes through the hot water heater, others don't.
You need to keep the hot water pipes and the cold water pipes separate through the house, if you start interconnecting them here and there you would end up with tepid water, neither hot nor cold, and very unacceptable. Even tho your pipes are connected all together at one place, the hot and cold stays separate exactly because you never connect those pipes more than the one location.
Same with the wiring. They found out, when you interconnect the bare ground and the neutral several times over, it kinda defeats the whole point of the bare ground wire, any flaws in the wiring the bare ground is supposed to catch become all mixed up in circular loops between the bare and neutral wires, creating 'tepid' situations that we really don't want.
This doesn't properly explain the electrical deal I know, but maybe it makes it easier to understand the concept of only one connection working best?