Similarly, seasteads will trade extensively with land-based businesses. The people who profit from those relationships will encourage their government not to interfere and drive away the seasteads business.
LOL That's classic. Because the economic bolstering of doing business with a community of a couple thousand people (at most) definitely outweighs the advantage of simply blockading food from the community and then seizing all the assets.
My question is, in this modern era, why should a nation-state try to grab a floating platform?
As someone already mentioned, the amount of illegal activities going on there would be more than reason enough. Couple that with the fact that platform is 100% dependent on imports and that it is absolutely helpless to attacks, and it won't last long.
Illegal by your country's law, but what kind of a nation pays real money and resources to go and impose their law on foreign lands?
Umm... have you kept up with the news for like the past... ever? The US and NATO invade and/or fire missiles at nations on the daily, simply because they don't like the government policies in those nations. Familiarize yourself with the military intervention history of the US. Do you remember the Panama invasion? How about the Bay of Pigs? Lebanon? Somalia? Nicaragua? Does Iraq ring a couple dozen bells? How about Bosnia? Have you heard what's going on in Afghanistan?
You think that won't also happen to a defenseless oil rig whose MAIN businesses will be things like illegal drugs, illegal weapons, tax havens, sex trade, child pornography, etc.