This has been hanging over the show for 3 years. Alex and Scott have been on the fence about leaving during that time, and Scott had only been re-upping for half the episodes, hence the frequent absence of Danno.

The show revolved around Alex/McGarrett, though. Much like original Five-O could not continue without Jack Lord (who seemed content to do it for as long as possible), Five-Zero could not continue without Alex, who started the role much younger than Jack, and therefore has more of a career ahead of him.

I'm sure Lenkov and CBS would have continued the series for years to come if this didn't occur.

I have mixed feelings about this. Despite its flaws, I enjoyed new Five-Zero overall, and felt they even handled the replacement of Kono and Chin pretty well. At the same time, the show has run its course, and it seems that most episodes are either caught in a formulaic rut or have ridiculous premises which make me wish for the formulaic rut back!