Upgrading with miles is absolutely an option (US50 flights) on this route at time of purchase. Either you are not logged in when you are searching or you are selecting a Basic Economy fare where the option is not available (you must select a Main Cabin or C+ fare to get the option). Note that this is nothing more than paying the fare diff between coach and F with miles at the rate of 1 CPM. If you have a DL Amex, you can basically get the exact same deal by selecting F fares and using Pay with Miles to partially pay for the ticket.
The basic problem here is that there is currently only J/C bucket availability on the outbound flights in March and C fares are about $2K one-way. However, there are a number of dates with D bucket open on the return flights from OGG-SEA with D fares around $700 one-way. Namely 3/4, 3/6, 3/7, 3/11, 3/14, 3/18-21, and 3/26-28. You could book the return flight if one of those dates works and hope that D bucket or lower opens up on one of the outbound flights at a later point (set a fare alert on Google Flights).
Alternatively, you could book SEA-HNL where there is pretty good of I/Z bucket availability at around $600 one way and a separate ticket from HNL-OGG. The Z fares require Mon-Thu travel (I fares are good for Fri - Sun depatures). Decent I bucket availability on outbound weekend departures in March.
And I will add we are flying on Wed (both outbound and return)… so the HNL routing does seem to work pretty good with decent fares w/ upgrades using miles. That was the other puzzling thing.. $4k for F mid week. I would sort of understand the weekend.