Karen has quite terrible parents. Are they weeaboos or something, not to teach their child English at all, despite it being their own native language? Their relatives are back in the USA, and they do visit the place, yet Karen isn't able to communicate there with anyone. Really thoughtless, but unfortunately such people exist and especially existed aplenty in RL. Especially in the more distant past, when a couple moved to a new, wealthier country to seek a better life, such as those moving from Europe to the USA, the parents often decided not to teach the children their own language at all, leaving the child only with the language of the new homeland, for example English. The idea was that the child would then both feel like and be treated as a 100% native one and not get bullied for being an immigrant/immigrants' child. Decades later in interviews or social media such children would then lament their fate of not knowing the language of their forefathers.
You'd think Americans, even if they moved to Japan, would understand that knowing English in the modern world is a rather useful skill. Sure, you can live in Japan your whole life without speaking English, but it would open new doors and make life easier.