One factor that makes boiled eggs hard to peel is freshness. The fresher they are, the more difficult. Eggs that are 3 weeks to a month old do very well, as the layer between the shell and the rest of the egg has broken down some. Edit: So my wild ass guess is the eggs on the shelf are fresher due to low supply. Since grocery stores normally sell first in, first out, you are getting the oldest eggs they have. If they don't have very much in stock, it's likely you're getting the eggs that just got trucked in.