I agree it's mostly the songs that contributed to it, followed by movies and maybe cartoons?
And it reminds me of another similar thing in pop music.
You see a lot of these "ticks" abbreviating words like 'round, o'er, hurtin', and so on.
I know poetry traditionally had such things to help with its meter (o'er, 'round, Tis, etc).
But the pop songs since the 50s and 60s brought about inordinate amount of abbreviating XXing to XXin', or even dropping the "g" altogether, both in transcription and pronouncing them.
Bob Dylan songs are full of these for example, so much so seeing "hurting" instead of "hurtin'" is downright rare.
I am just wondering whether it makes it look cool to most people, and if it's mainly Bob Dylan who introduced this trend or does it go much further back.
And how do mainstream people feel about it? Do you find it interesting, or even enriching, or does it just annoy you?
They didn't bother me much when I was younger, but as time goes on I seem to frown upon them more - I guess I'm getting more conservative :-)