Where did all the gentleman go?

Today, I was walking into the library at school. The bell had just rang and so everyone was still piling out of the library. There is only enough room for one person at a time to go through the detector (right before the door). And as I patiently waited my turn, one young man stopped and waited for me to go through. I got thinking about it, and I realized that while I was standing there for a while, most of the people who went through the detector were male. This got me thinking, because back in the day, the men would always let the ladies go first. They would hold the doors, and would show their consideration, and just be a gentleman. But I waited for a while and none of those guys even waited for a second! And I can't help but think about how many doors I walk through, how many times the guys shove to the front of the line-to get to the back of the bus, to get out of class first, to get into the cafe line to make sure they get the good food.
Do guys not realize that it's the little gestures that catch our (us ladies) attention? That flowers brighten our week, that holding a door makes us feel special, that kissing our forehead makes us feel like a princess. It's these littles things that stand out.
Even though it was a little gesture, waiting for me to go through the door, I will always have some respect for him.
But my question is, why did no one before him stop? Why do I have to get shoved back in line for the bus? Where did all of the gentleman go?