Why do some folks have such hazy memories of their childhood?

I remember most of mine from the time I first set eyes on my new sister, when I was 3. That may be my first memory.
I remember a bed shaking in the middle of the night around that same time. Mom said it was probably an earthquake.
I remember playing with my best friend, who lived next door. I remember her mom spanking me for something her kid did! She spanked her kid too, but I was outraged at being blamed for any of it.
I remember my friend’s little brother, Randy, used to watch TV, lying on his back with his head pointed toward the screen.
I remember, “Silly Wabbit! Trix are for Kids!”
All of that was before I was 4.
I remember lots and lots of stuff. If I focus on one particular memory, other memories come in around it.