Hobbit Movies

Hello!

I was thinking about the Hobbit movies and wondering why it was turned into three movies. I know that the biggest reason is probably profit. They wanted to get as much out of that series as they could. However, I find one thing curious. Most of the time, when turning books into movies, the biggest reason they cannot put something into the movie is time. So why is it that, even with three movies and each movie being about three hours long, they changed the story so much? I imagine they put Legolas in because they wanted to connect it even more with LOTR. But there were quite a few changes that I didn't see as necessary. For example, we see Radagast in a number of scenes in the movie, but he is only mentioned by name in the book. I just find it curious that even with all the time that they could ever need, they still changed it from the book in such a large way.