This is a popular take here, but IMO it's not accurate. The 5s are not "completely ignored on offense" because that is what we do. Our 5s are just not skilled and strong enough to post up, maintain position, catch, and then have the footwork and touch to finish. Similar reasons as to why they are not looked to on the pick-and-roll (other than poor execution). They have to have the space to catch and go right up without a dribble or footwork execution. Otherwise, they just can't seem to finish.
Bring in a 5 with size, strength, and skill set and they will be a big part of the offense (Sr. Christmas, Arinize, Jackson).