3 weeks post lower face/neck lift. Left ear is popping and occasional pain. ENT removed small scab. Why is it still happening?

The issues you describe are not unusual and things will improve. Often small amounts of fluid get into the ear canal and this can alter things. Pain and tightness will improve but can take a few more weeks. Often by 6 weeks the pain / tightness things soften considerably

Is it possible that internal sutures were placed near the ear cartilage or temporomandibular joint that is causing this issue?  If the sutures are dissolvable this issue will likely resolve.  If permanent and you continue to have the same symptoms without improvement, they may need to be removed.  

Your surgeon may need to remove internal sutures if they do not dissolve.  They may be placed near the ear cartilage of temporomandibular joint.   Follow up with your surgeon.  Best to you!