Why is it called Pollyannas, though?

I don't know. Probablly because the original Pollyanna was so sweet and was happy with whatever was given her, or something.

It was a book about a girl who was totally, annoyingly optimistic about everything until she gets hit by a car and is sad until she realises she got the whole town as annoyingly optimistic as she is. It was also a Disney movie starring Hayley Mills. :)