What I think-
Think RASM.
Big driver for airlines and their shareholders is RASM. Gotta increase RASM in any way possible. However, flights from mainland to/from the islands are RASM killers. They are some very long stage lengths. So, how do you offset that?

These flights are frequent flyer miles/points cache dumps. A significant amount of miles/points are used during trips to/from the islands, and the airlines love shedding those miles off their books. This way the airlines can keep higher fares on shorter flights with any significant higher RASM. Think MSY around Mardi Gras, AUS during SXSW, LAS for CES, Super Bowl, or any other event that creates a big spike in demand for air travel (thus higher fares). In addition to a significantly higher fare, increased service also is common to these high yield events. For example, what was once a 3x/day service now becomes a 5x/day and the airlines ASM increases by 66% with a RASM increase of 85%, (hypothetically). If passengers use miles/points during these high yield events destroys RASM. Especially when the airline advertises “No Black Out Days!”

But with the addition of Hawaii flights, there will now be significantly less miles/points for customers to burn through.
The actual cash money brought in by AAL, UAL, DAL, AAG, etc is significantly lower, when considering the distance flown.

The only real revenue generation with these flights comes in the freight/mail in the belly.