I think they are making all these Tolkien movies because they’ve already built most of the sets.
That.
And probably ten billion dollars in sheer profit.
This is the strategy that Gene Rodenberry used to get a Star Trek series back on television.
He figured that if he could get a Star Trek movie made it would drum up renewed interest and all the props and sets (mostly) would just be sitting around all paid for. Seems to have worked like a charm.