Having worked stock in a grocery store, this is part of it. After asking alot of different people at different levels, the consensus is that shelf space is also paid for by many brands, and what space goes to who is decided way above the store level. So once in a while the stockers get paperwork that moves a ton of stuff around, and no one who works in that location has the authority to say no. Sure, sometimes a manager will do that anyway, but they always have a reason, and it's usually something about the reality of the store configuration, like not putting too many cold items near warm areas, to keep humidity down and reduce spoil.