To play the devil's advocate, it is possible they simply haven't coded in any conversation benefits from the Backgrounds.

Also, Backgrounds (officially) are more than just a couple of Proficiencies. They typically include Proficiencies, Tool Proficiencies, Languages, starter equipment and a Feature of some kind. Now obviously some of these would have less benefit depending on the setting. I mean, if you're an Acolyte in the Deep Desert, the Shelter of the Faithful Feature is probably of next to no use to you.

The benefits are more social than anything, and that takes work to pull off. Doubly so in a computer game. So its on Larian to have a decent number of conversation options where our Background come come into play.

Pillars of Eternity (for example) someone did the math to determine how many conversation checks there were based on your god. Each one had like a dozen over the course of the whole game. Some had more, some had less, but I think on average, most had around a dozen.

So it CAN be done. It's just possible (giving them benefit of the doubt here) they just haven't coded these things into the game yet.