I would imagine that Peter used to be a bit easier to reach and more outgoing. However, this could have resulted in him going and trying to talk to people that were not particularly firm believers and having them potentially freak out. I mean, if you just did some little thing like sing a song by your window and all of a sudden some seemingly random boy came flying in with a little fairy and you were not a 100% believer you would probably freak out. This probably lead to some people panicking or even maybe doing things like screaming or even running away when Peter came.

Think about it from his point of view, if people are sometimes scared when you come, wouldn't you want to make sure that you can really trust them before you do? That is possibly why it takes a bit of time for Peter to come to people.

Remember, have faith and trust and he'll bring the pixie dust.

~SeaOfMoonlight