Anyone who's driven through west Texas knows that this is not only nice to have but necessary. Rolling hills for literally most of a full day of driving. It's among the most boring drives EVER.
There's nothing wrong with increasing the speed limit in the wide open spaces. I have driven through west Texas a few times (lived in Midland once, well twice actually but the first time I was a little kid and my parents wouldn't let me drive ) and the drives can be long and lonely.
Lower speed limits are for areas where you have windy roads, congested traffic, school zones, city limits, and reduced visibility.