Well strange you mention this certain topic, I wrote a hub on dreams.
I read that keeping a journal is the best way to remember, however being one that has dreams that foretell the future to some point I never have/had a problem with that. I still remember dreams from years ago like they were yesterday and I also have dreams that were aiding to friends.
I also dream of global events at times. So this is a rather difficult question for me. I am given dreams through the unknown. I am given messages.
You are right though, many people do not remember their dreams long enough to keep a journal. I feel that if we do not remember them then they were not important at that given time anyway.
I would not rack your brain trying to remember, if they are meant to be remembered you will. They are given to us by God/angels and given at the time we are suppose to know something.
In the bible it says, God will give dreams and visions to many just before his second coming. God chooses certain people to receive his messages through others or leads them somewhere. I believe he does this with our dreams as well.
If you are that keen on remembering them, you can always ask for help with them. (I do not know your beliefs, but just giving you an idea).
Sometimes if you mediated when you have some time alone, this helps as well.
Have a good day