Hey Happy Days fans I have a question which is only out of curiosity. I noticed that in the first two seasons of Happy Days they used the Bill Haley Rock Around The Clock song in the opening why didn't they used that for the closing credit as well just asking.

I don't know their reason for this, but Rock Around The Clock is the type of song to kick off the beginning of a show, not an ending. Also shows with different opening and ending themes aren't unusual.