Why did they make RoP

As the title states, I’m wondering why the show was made, since Amazon could only buy and use the hobbit, Lotr with appendixes. I have read somewhere else that the estate would not sell silmarillion. Amazon wanted to make a show about the second age, but why did they make it on these premises, as the source material is really thin?? I’m wondering if the limitations to the source material is a reason to the shows lack of quality….