Why do they only let certain people in the establishment? The door's are locked in the morning and at night. But only certain people are given access to go inside. ???

Unless you know for sure they aren't employees, they may close the inside access for select hours.

The door would only be locked to the public if they couldn't use the dinning room for some reason or because the store is understaffed. They dont do it for themselves, and the people going in are most likely employees.

It looks like it is open 24 hours, but may not have the dining area open 24 hours. The other possibility is that staff lock the doors when they need to take breaks or use the bathroom.

I go to Tim Hortons in sanborn around 4:45 am and never have a problem getting in