

I wouldn’t necessarily blame the writers for the shift. The bigwigs making the decision believe that using existing IP means that half the marketing job is already done.
I don’t blame them for the shift at all, that’s all on the higher ups who only see dollars. I do however blame them for doing things like not engaging with the source material and actively changing character personalities to fit their own idea of the story. Specially when it is so drastic that it goes against the overall story and it has to be retconned or explained in unbelivable ways.
(Yes I’m still bitter about The Witcher show)
It’s not like he sat on his ass before then: He went to Oxford until his early 20s, then WW1, illness, working on the OED, working at Pembrooke, translating the Green Knight, Sir Orfeo, etc. his work on translating Beowulf drastically changed how it was percieved(before he pointed out the poetic nature, it was viewed as a childish tale of monster battles).
Not to mention that he was writing LOTR in stages during WW2, and he was a lecturing professor at the time.