IMO, the expectation that Garmin would keep AC in the form that existed at the time they bought it just did not make any sense, despite what they may have said at the time. Why buy something that someone thinks has value (why else buy it) if you are not going to turn it into something that gives you a return on your investment? Corporations rarely give stuff away for free. It kind of goes against their fiduciary responsibility to their shareholders.
AFIAK, Garmin is not a charity. They see AC as an asset that they are going to exploit. If Jeff merely wanted to provide a service to the boating community for the greater good and wasn't looking for a return on his investment, he never would have sold AC to Garmin. I don't know what he sold AC for, but at the very least he seems to have gotten a new boat out of the deal.
Not that I'm knocking what he did. He came up with an idea and made it work (and probably spent a whole lot of time getting it there). A lot of people bought into that idea and made it something of value. When the time was right Jeff took the money and ran. It's the American way.
If all those people didn't put their whole life on Facebook for free, Facebook wouldn't be worth squat. Same thing happened with AC. Jeff got a lot of people to supply information for basically nothing, and then sold their contributions to someone else. Good for him.