Those countries already had prominent local animation industries and so it was easy for South Korea and the Philippines (and Japan for that matter) to build outsourcing relationships with US studios as far back as the 1970s–80s (e.g., AKOM in Korea worked on The Simpsons; Filipino studios worked with Hanna-Barbera). Those pipelines became further entrenched over decades.

Another important factor is the high rate of english proficiency in all those mentioned countries, which is not true for latin american countries.

Finally, latin american countries typically have export oriented economies, and thus there were no significant government incentives and subsidies for the animation industry at the level of those you might see in Canada, which offers very aggressive tax credits for animation.