"Why is Gojira in Japan?"
That's like asking why Batman is in Gotham.

For those wondering, this is from the cartoon series that was based on the 1998 American Godzilla (the one that Toho officially calls "Zilla"). There's something of a general agreement the cartoon series is many times better than the movie it used as its basis (and IIRC wasn't this one of the last "Saturday morning cartoon" animated series that used a movie as its basis? I remember there was once a point in time where that was a fairly popular thing, like Beetlejuice, Real Ghostbusters, and even Addams Family got a cartoon in the 90s after the success of the live action movies [they even got John Astin, the man who played Gomez in the original 1960s tv show, to reprise the role in the cartoon]).