In most television shows and movies what people are looking for is somebody that represents them - call it an "avatar" if you must. When kids watch Sesame Street they relate directly to Elmo.
He's younger, smaller, has an insatiable curiosity, and is in a permanent mode of questioning and discovery. He even has similar mannerisms to children - he laughs a lot, has lots of energy, and is frequently confused as to what's happening around him.
The reason the author doesn't like Elmo is because Elmo acts like a two year old. The reason two year olds love Elmo is because Elmo acts like a two year old.
Sesame Street was created for two-year-olds, not bitter Internet pundits.