You can't remember everything

 https://www.youtube.com/watch?v=diyoTo3Co08

Research suggests there's a reason you can't remember much from your childhood: new memories are replacing the old ones.

Another reason: One doesn't have traumatic memories.

I feel the reason why I still remember is - I have traumatic experiences which I have found consistent with my life since childhood, and over time, these have become reinforced.

Perhaps memory replacement is a happier, less stressful, anxious or depressing thing.