Why capture an american?

Since when dies America have jurisdiction to go after ships registered in Liberia or Panama, owned by a consortium of companies in several other countries, chartered by a Taiwanese company, carrying Chinese cargo, insured by a multinational consortium, etc?

America can set all the rules it likes for ships flying the stars & stripes. And it does. And that is why most companies, not liking those rules so much, register their ships in other places. So they are not bound by American rules.