The question of whether Polish is 'useful' or 'valuable' outside of Poland is irrelevant. If you're in Poland for an extended period of time and don't speak it, you're basically a loser and putting yourself at other people's mercy and willingness to communicate with you.
Personally, I found corporate expats (business people stationed in Poland by their companies) to be a dreary bunch when I rubbed elbows with them in the 90's. Their primary non-work activity in Poland is to create a separatist bubble and pretend they're not in Poland.
Other people, here on their own initiative and not supported by an inplace infrastructure and group of employees paid to make things easy for them, have to learn Polish well enough to function (just what level this is will differ on a case by case basis).
A slight exception is a certain kind of (usually, but not always, British) English teacher who regards Polish the way missionaries regard pagan idols and sacrificing virgins to volcanoe gods, as a backward practice that needs to be eliminated (to be fair, I've only met a few of these, but they absolutely do exist).
American monolingualism has a lot of causes and the idea that Americans don't have to learn foreign languages is probably a minor one. The two more important causes are the fact that as an immigrant culture without much shared history (relatively speaking) Americans aren't bound by the kinds of common experience that, for example, Italians are. A common language (American, not 'English') is one of the few cultural symbols that hold Americans together.
Secondly, the immigrant experience has caused that Americans often cannot distinguish between visitors and immigrants (or between non-Americans in their own countries and immigrants). Part of the immigrant experience is the idea of using any other language as little as possible and English as much as possible. Americans tend to unconsciously treat anyone they meet abroad as a newly arrived immigrant, still ignorant of our ways and in need of encouragement (or coercion) to speak English to better assimilate.
(Added: Another factor is that English speaking countries have _terrible_ English classes for their children. While English speakers have amazing dictionary making traditions, they have the worst grammar writing tradition of any European language. What was traditionally taught in schools as "English grammar" is nonsense. It's unworkable and unteachable and demonstrably false but if you try to update it, the traditionaists scream bloody murder. The result is an appalling ignorance of how _any_ human language works and university English majors who don't know the difference between an object phrase and an adverbial phrase (and the cycle continues).
Finally, some people find language learning to be a valuable intellectual exercise worth doing for its own sake quite apart from questions of later payoff or exploitation, and others don't. I belong to the former category and fuzzywickets probably belongs to the latter.