LotR - Prologue

[Firefoot]

I wonder why the Prologue could not have just been part of the Appendices?

From Concerning Hobbits:

This book is largely concerned with Hobbits, and from its pages a reader may discover much of their character and a little of their history. (...) Many, however, may wish to know more about this remarkable people from the outset, while some may not possess the earlier book. For such readers a few notes on the more important points are here collected from Hobbit-lore, and the first adventure is briefly recalled.

So, in short, I think that JRRT's purpose in making this part of the prologue and not the appendices is to give readers a background on hobbits, which I think is especially helpful for some people who, for example, just picked the book up off the shelf randomly. For people who are familiar with the books, the information would be just as helpful/interesting in the appendices, but I think that Tolkien wanted to give people some background so that they wouldn't be completely confused (especially, as he points out, for people who have not read The Hobbit). I know for a fact, however, that one of my friends skipped the prologue and then went back to read it after finishing the book, and found it much more interesting because she had a better idea of what it was talking about.