You know that feeling you would get every time you nearly run out of breath underwater? You wouldn't be the most rational person and would do anything to get out of that situation even if you know it might kill you only after an extra 10 seconds. You wouldn't care if the only way to get out of the water would be into a deathtrap, the very primal urge to get out of that situation trumps all.

Since we know human beings aren't the most rational during stressful situations like these, when the buildings were on fire, most people were pushing each other aside just to get a breath of fresh air. The smoke inside the building was pretty much unbearable to the point where a single gulp of the very little fresh air you had out the windows felt like the only thing you ever wanted in the world.

Of course, you've got 20 other people pushing each other for the same window while the others are already jam packed with people from the upper floors. Some used the window to signal that they're still their, others for a quick relief. But the pain of just having a second of simple relief and then being pushed back inside to breath in the unbearable smoke led some people to just get out and jump, others were even considering hanging outside the window only to fall or get back up realizing it was a bad idea.

In the end, the people who fell weren't thinking about a quick death, they just wanted a relief from the smoke and only accepted the fact that they would die because of it. Those people couldn't stand their lungs filling up and choking them with smoke only to get a second's relief, they just jumped because their body is telling them anything is better than being in that room.

It also didn't help that the smoke was flowing out of those very windows they were breathing out from, meaning those that got lucky spots on the sides of the windows were subject to the same, probably denser amount of smoke.

It was a fucked situation, and It just sucks what people will do when you put them in that situation.