A Door Able In Security

I went to sign a paper yesterday on the 3rd floor of a bank building. It was at a business separate from the bank that occupies the first floor. But I had momentary trouble getting inside. The middle pair of the outside front doors of the set of four were locked. So I tried the left most door. Unlocked, fine, I was able to enter the building. There is another inner set of four locked doors to the bank lobby. Eight doors total, with an open foyer between the outer four and inner four.

A Visual:
[all four outer GLASS][ doors, locked or ][unlocked, open to][ the exact same foyer]

I was curious about why some of the outer doors were locked.

I knocked on the locked inner doors (it was late enough in the afternoon for the bank lobby to be closed) and a bank employee came over to talk to me. I asked why the middle doors of the 4 outside doors were locked. She told me they were for bank customers, and the bank lobby was closed, and that the left outer door was for the businesses on the 2nd and 3rd floors. I asked her if she thought this situation was funny. She said "no".