There are many constraints to satisfy, and avoiding hills is but one of them.

Most of us would take a hill with a protected bike lane over a flat 45mph.

In my experience, Google Maps too often sends me down dangerous streets - busy, wide, arterials with fast moving automobiles.

Though I do know some people who prefer them because they can be a little faster. Not worth it for me. I'd much rather go a little out of my way for a comfortable safe ride.