Of course you’d plan to structure the episodes in a way that made sense to the format.

But you’re adapting an existing story which already has a beginning, middle and end. It’s much easier to split this up into two than 6+ if you want to keep to the original story. It’s different when you’re creating a new story from scratch specifically for the format, which is not the case here.

And what evidence do you have in saying splitting a book into movies is easier than doing so into episodes? Just because there are more episodes than there are movies does not equate to difficulty. If you planned for it, it would make just as much sense as a movie.

It’s more difficult because there are more opportunities to fail, and you have to get more things right. You can’t just focus on each episode, you also have to make the whole thing together a good experience. Doing so for two movies is much easier than 6+ episodes.

It boils down to a simple truth: making something smaller good is easier than making something bigger good. A movie is bigger than an episode, but it’s smaller than a series.