This might be a direct consequence of language; in Spanish, when you ask questions like this you are normally specifying whether you expect a single or multiple

This might be a direct consequence of language; in Spanish, when you ask questions like this you are normally specifying whether you expect a single or multiple answers by default (akin to "what thing(s) make life meaningful", noting that you can ask with or without the "s" but that is a choice). In Japanese, singular and plural are not distinct except in very particular situations, and IIRC the singular is normally the default unless context makes you think it's plural, so I expect this to contribute greatly (akin to "which makes life meaningful?"). I don't know Korean to comment on that though.