Because this cruise, and the other longer cruises, are not like regular 3,4 and 7 night cruises. There will be so few children on this cruise that there will likely not be the same demand for things like Princess and Frozen M&G. And the character breakfast went to ticketed because of the sheer number of people wanting to participate, more than could reasonably be managed in the dining rooms. That won't be the same on this cruise. Like I say, I am not 00% certain, it is supposition, the same as everybody else but that is my gut feeling, based on what I know from having taken this cruise before
We prebooked our character breakfast as well as character meet and greets for our last cruise which was 12 days. You very could be correct with the MUCH smaller kid demographic on this cruise, but it seems a little strange that Disney would change now-standard procedure for one or two cruises. Not that what Disney does always makes the most sense.
Yes, many times port adventures are only seasonal. Whale watching in certain areas like you mentioned and bear watching in Alaska are a couple. The one we are planning is not seasonal. We may just be extra adventurous and book it directly without Disney if it comes to that. Still many days before our cruise. A lot can show up between now and then.