Comment by qwery

I'm not sure that such a path of least resistance will necessarily be obvious from the outside.

Likewise, I'm not sure that (from the audience's perspective) one can so easily infer simple and exact reasons for why an adaptation differs from the source material.

I'm sure many of the people hired to work on a film, adaptation or otherwise, do want to have an impact on the production, or 'leave a mark'. Deviating from the source material might even be the path of least resistance.