Because even the U.S. does not have infinite resources.

Why does it require infinite resources?

Edit: I'm being glib, but seriously, this isn't necessarily a resource-intensive issue for the US to engage in. This kind of thing should be achievable purely through diplomacy. Surely there are some attractive incentives a nation like the US can bring to the table in the interests of compelling a nation like the Philippines to clean up its act, you know, like bringing a Nike executive to the meeting.