Going faster just simply requires more fuel, and fuel is a precious and limited resource. There are some optimizations we could make to aircraft design to improve fuel economy, but we've already done most of the optimizations given our constraints of safety standards and the general goal of comfortably transporting humans.
The rest of your post is pretty accurate, except for the goal of comfortably transporting humans. That "comfortably" is suffering the death of a thousand cuts.
Going faster just simply requires more fuel, and fuel is a precious and limited resource. There are some optimizations we could make to aircraft design to improve fuel economy, but we've already done most of the optimizations given our constraints of safety standards and the general goal of comfortably transporting humans.