It's not actually that hard to do, although quite a lot of people do seem to have problems for some reason. I am not sure why people find it so difficult and who, if anyone, is to blame. Maybe we have just become so wrapped up in our own lives that we've forgotten how. Also, if no-one congratulates you or compliments you on being so polite when you are younger, or if they are not polite or chivalrous in return then you start to think "what's the point" and don't bother with it. Because no-one is polite to you, you're not polite to anyone else and so it continues.
This is why I always make a point of trying to be polite myself. Every time I say thank you, or hold the door for someone, or pick something up for someone when their arms are full, I am throwing a stone. That stone may simply bounce off of the ignorance of some people but with others it'll land in the pond of their subconscious and as the ripples push out into their conscious mind, maybe they'll try it too and then more stones are thrown and the ripple spreads from there.
Basic chivalry is easy too; you don't have to be a knight on a charger either. Simply hold the door for someone, if a door opens toward you and allow them to pass first. If someone has their arms full and they drop something, help them to pick it up. It really is simple stuff!