Why do 24-hour convenience stories have lock on their doors?

The answer should be easy, when you want to buy the door, you don’t have to buy this one with lock, that true, but there are such situation that bull you to close them, like holiday, every events. If shop is open 24-hour every per day, that doesn't mean that he can be never closed. In Poland market, which function like this- open all day, they are close at night, there is only small window thought which you can buy things you need to buy, at night.
It is always better to have a lock, it’s more comfortable and useful.