I have a serious concern. What causes your inet on your fone from working or have no connection to your isp in a specific building?

Usually military and govt. offices have blocking capabilities yes? Then why is Krogers blocking my internet but connecting me to there wifi? Am I missing something? I literally had no inet in store unless I connected to their wifi, which didn't use to exist but now does. It's not like walmarts where they suck your battery dead, but still is a concern.