Então os monstros são apenas uma representação de quais são as conseqüências das ações de Gloria. Eles não são reais.

É interessante saber sobre a violação de direitos autorais da outra resposta. Mas você está se perguntando por que algum país asiático aleatório. Deixe-me tentar responder a essa parte.

ref - Colossal explicado

What’s up with Korea, why Seoul?
Well, Seoul is the opposite side of the Earth to America. There is a 12 - 13 hrs difference in time zone between the two places. Metaphorically it’s a place which is behind Gloria, what she can't see. Something that is not in her area of vision. When Gloria ends up doing something, it affects a lot of people. She doesn’t see that it affects others. The monster appearing in Seoul and hurting people is indicative of how her actions have consequences on others that she is not bothered about.

Então, uma cidade asiática aleatória porque suas ações estão ferindo pessoas que ela não conhece e não consegue ver isso. Mas quando ela começa a ver o que o monstro faz no noticiário, ela começa a perceber lentamente como seus modos irresponsáveis podem causar muito dano não apenas às pessoas que ela ama, mas também aos outros. Outros ela pode nem saber.

Razões legais

A intenção original era que o monstro ficasse furioso em Tóquio, no Japão, como uma comparação direta com Godzilla ... mas a produtora foi processada.

Telegraph.co.uk

However, there is one film Colossal’s producers are keen to avoid comparisons with – Godzilla. Last year, Toho, the production company which owns the rights to Godzilla, sued Colossal's Voltage Pictures for trademark infringement after they used pictures of the Japanese behemoth monster to promote their film. According to The Wrap, an email to investors at Cannes summed up Colossal with the phrase "Tokyo is under attack by Godzilla and a giant robot.”

Vigalondo had previously been quoted as saying he would make "the cheapest Godzilla movie ever", but after an out-of-court settlement all references to the radioactive lizard were dropped, and the film’s location was moved to Seoul, far from Godzilla’s traditional stomping-grounds.

Deadline.com

Japan-based Toho sued Voltage for copyright infringement in mid-May as the company was shopping Colossal around the Cannes Film Festival. It wasn’t hard to see why as Voltage’s pitch included photos of Godzilla movies and Vigalondo was quoted in an interview that he was going to make “the cheapest Godzilla movie ever.” Hathaway stars as a woman who moves back to her hometown after losing her job and boyfriend — only to discover that she is somehow strangely connected to a giant lizard-like monster that materialized over Tokyo and is wreaking havoc on that city. Dan Stevens, Austin Stowell and Tim Blake Nelson also star.