Online only freemium games are the top money makers for mobile. That's what the devs of seabeard specialize in. The fact that people like it enough to wish for an offline version, raer than just saying, "Online only? Oh well, not playing it," shows that the devs are good at their craft and are making enjoyable games. But if you don't have constant net access and don't want to pay a few bucks here and there over the life of the game, then you just aren't the kind of player that thus game was made for, and to be brutally honest, the devs couldn't care less about your frustration.
I'm not trying to be rude towards you or the devs in any way, so please don't take it that way. I'm just saying that the game industry is just that, an industry, so each developer comes up with their own strategy for generating profit, which means their product will not be designed for everyone.
There are plenty of wonderful games on iOS. Don't waste your time being frustrated with this one.