Agree with others who've noted that folks flying to/from the islands are willing to buy up because its vacation/self/etc. so getting stranded at #1 or #2 on the upgrade list is not uncommon on full-ish flights with domestic F-cabin demand.

Also, sometimes, you get offers for your upgraded seat even after the F cabin is sold out: 04/27/18 LAX-LIH 752 8:15 AM depart (& LIH-HNL on HA), the update and the followup/$300 buyout.

David