I agree with the OP there that backgrounds universally giving bonus languages is weird, even if those backgrounds are only for demonstrative purposes. In 5E, some backgrounds give no languages and only tool proficiencies, because narratively it doesn't make sense for them to give languages. You can explain a Sage or a Noble learning extra languages as part of their training, but why should a Sailor learn an extra language while living in the streets? Why does being a labourer grant me Dwarvish or any other language automatically? Even if I grow up in a monocultural town, why does my background make me bilingual automatically?
I think they chose this path because they decided to standardise a few things in Backgrounds even if narratively it doesn't make sense (both a Noble and an Urchin start with 50 gp worth of things, every background grants one Language and one Tool, every instrument costs 20 gp and every tool costs 5 gp etc.). I'll already mention I don't like this general trend in my feedback to the playtest, but since this is the general trend, I doubt my opinion will change much.