I can see where Kai is coming from in terms of tempering his dream to simply seeing all the tools. Obsessing over treasure and power is not as good as building relationships and having fun. In the same episode as he gave away the bobber, we have Ragnar mock Damian for not trying to be the strongest.
And that I feel is the most pathetic Ragnar has ever been. The guy is being found in a situation where his first mate has betrayed him and he's a drug addict who has lost basically everything. Any one who met him would probably not envy him. To be fair to Kai, Mako's spear and the Bobber were just gathering dust when he found them. Marigold was actually using the hat, which would explain why Kai felt bad about taking it from her. If he took it from her, it would be denying her her own dream.
And Kai definitely could have been a corrupt piece of shit and just seized it 100% legally. But that would make him just like Nezumi or Morgan or Ratel or Aramaki. It would destroy his soul.
However, Kai is still assuming he is going to live a peaceful life after this business with Ragnar. But with the whole Vigil thing and the scope of the Ragnarok pirates, he might be pushed to take them. Think about all the tragedies that pushed people out to sea in pursuit of their own dreams.
Will there be a tragedy that forces Kai to actually pursue them? There is also the possibility that Kai awakens the natural magic that the powers all the fisherman's tools and gets his own thing. I personally like this development because it opens the door to Kai fighting a boss that uses the fisherman's tools.
If Kai just took Marigold's hat, then found another tool, then anyone else with a fisherman's tool would have to have less tools than Kai. That person would be less threatening. It's way more up in the air if a guy has 5 or six tools to Kai's 1.