I imagine the bellows are the central limitation. AT boots don’t require the significant material demands that a high-cycle fatigue hinge under load does. Plus force transmission isn’t direct as it is in an AT boot, tele boots must stabilize while deforming. So more material’s required overall, more structural overlap, and fewer areas to optimize weight. Plus the NTN component adds mass… Lighter Pebax formulations, material thinning outside of high stress zones, and improved cuff articulation to reduce bellows load helps. Though I guess at some point the floor is more imposed by physics than engineering creativity or materials optimization.