I get your point. Luxembourgish is indeed useless outside the country.Is Luxembourgish considered an important part of the country’s identity? Because on purely practical terms it makes little sense to learn a language spoken by less than 0.5m people located within a small territory. Learning a language requires time and effort which might be spent on acquiring other crucial skills.
I'm obviously not suggesting that little countries should drop or replace their languages, but there are many folks who simply and practically see languages as a means of communication with others and do not associate it with 'culture'.
But when you live or work in that country, it's still worth learning the language.
I personally could not imagine living in a country and not understand the language spoken by a large portion of the population or in important media or institutions. The main radio and TV stations are in Luxembourgish, as well as discussions in parliament or the election campaigns. It's a question of integration into society.