Arnold Kling has a paper (PDF) which is directly relevant to the political motivation for seasteading:
In this essay, I will suggest that competitive government might be better than democratic government at satisfying the desires of the governed. In democratic government, people take jurisdictions as given, and they elect leaders. In competitive government, people take leaders as given, and they select jurisdictions.
The first part of this essay reviews some relevant literature. The second part lists some of the performance shortcomings of democratic government. The third part argues that competitive government could overcome these shortcomings. The fourth part considers possible arguments against competitive government. The fifth part looks at various proposals for implementing competitive government.
Seasteading can be considered a proposal for implementing competitive government. In my opinion, it is the most likely way for competitive government to ever happen. Not because the problem of settling the ocean is easy, but simply because it is less defficult than getting democratic government to relinquish control. After all, current governments profit from lack of competition, and have used those profits to entrench their power. Starting on a new frontier, while it means a lot more work for us, is the best way to bypass current power structures.
The paper includes a great quote from my dad:
“Imagine buying cars the way we buy governments. Ten thousand people would get together and agree to vote, each for the car he preferred. Whichever car won, each of the ten thousand would have to buy it. It would not pay any of us to make any serious effort to find out which car was best; whatever I decide, my car is being picked for me by other members of the group. Under such institutions, the quality of cars would quickly decline.”
–David D. Friedman, The Machinery of Freedom (1995), p.132
An obvious question to ask when contemplating shrinking the size of government is whether a large size is necessary to get economies of scale on large public goods such as self-defense. One possible political structure for seasteads is a hierarchical system like feudalism, in order to get economies of scale for large things while preserving local autonomy. In other words, local seasteads would set rules for things with only local impact (gun laws, zoning laws, building codes), while larger groups would take care of larger problems (like defense). In feudalism, only territory on a border can potentially switch sides, but with modular seasteads, any member could change jurisdictions. This will lead to more competitive pressure and thus more efficient government, while still retaining the benefits of large groups for defense.