Why do businesses have double doors if they keep one of them locked? Why do they keep one locked. It drives me nuts to try to open a door and I have to open the door next to it because it is locked. Why not just have one door?

Bigray in Ok

Sounds like a fire hazard. I don't really ever notice it, maybe it's a small town thing?

First world problem?

Sometimes they want more display space so lock one door to place goods behind it. In that case there should be a sign "Use Other Door" on the glass.
There's also an outside chance if it's a C Store where they leave one locked to prevent a rapid exit with a case of Bud under an arm. In that same vein, maybe the person behind the counter wants a better idea of who isn't a regular customer by seeing if they pick the right door when they come in. Hey if I worked nights in some of those C Stores I'd use all the tools in the kit there...

Double doors sometimes exist simply because it makes it easier to deliver large items. When one is locked down, it is nice for it to be marked.

It annoys me, too. I always pick the door that is locked.

Sounds like a fire hazard. I don't really ever notice it, maybe it's a small town thing?

I encounter this nearly every day in Oklahoma City including tonight at the exit doors to Jason's Deli on Northwest Expressway.

Bigray in Ok

It could also have something to do with how the wind is blowing and whether the wind would catch one of the doors.

Some covenience stores do that to slow down robbers / shoplifters on the way out.

It's also used as a ventilation tool to cut down on wind blowing through the store (the better stores use an air curtain to curb this and to keep bugs out) or the door is just simply broken and has not been fixed yet.

Even more annoying - a door that obviously has a 'pull' handle - but its a 'push' to open door.

On the double doors we had where I worked, one door unlocked with a key, but the other door was unlocked by flipping a couple of levers near the top and bottom of the door. It took too much effort to unlock. Plus, someone could throw their back out bending over to unlock it.

They do it to get a laugh out of customers banging into the locked door.

If both doors are required for a means of egress per code, locking one where you cannot use it as an exit is a big no-no.

It's also used as a ventilation tool to cut down on wind blowing through the store (the better stores use an air curtain to curb this and to keep bugs out) or the door is just simply broken and has not been fixed yet.

This is exactly the reason the wind.