I doubt if we will ever get to know the real truth about the cancellation (which I am very skeptical about) unless some whistleblower pops up in the future. The powers that be were falling all over themselves when the show was cancelled (with such short notice) that "it's been a wonderful experience," "everyone worked so hard," "it was a big success," blah blah blah.

It was mentioned in this video that the ratings had dropped from when the reboot first started. If they had continued the show with someone else in charge like that new guy, Lincoln Cole, maybe the powers thought that they were taking too much of a chance considering the production costs of the show, etc., etc. I would like to know how much the ratings dropped on Blue Bloods which was also on Friday nights compared to when it started.

One of the reasons the show was so successful on Friday (usually a graveyard slot for TV shows) was because there was no serious competition against Five-Zero. It's almost as if there was a "gentleman's agreement" with the other networks that they weren't going to run anything against it. Even if they did, and the H50 ratings were, let's say 6.0, and their competition knocked it down to 3.0, then 3.0 for their own show would still not be good enough ratings to keep >that< show on the air. So Five-Zero sort of had them over a barrel because of this.

I dunno why they had to get this Lincoln Cole dude to replace McGarrett. I'm sure that Caan would have left if O'Loughlin left, couldn't Grover have taken over? After all, he was the boss of the SWAT team before. McGarrett could have dropped in once in a while for an appearance without any crazy stunts just to keep the fans happy.