I don't tell someone they are playing the game wrong.
You and I (and our tables) just have very different approaches.
There are a core set of backgrounds that players can chose from. There's no problem with any of them. You can chose them for whatever reason you want- a good reason, a bad reason, or no reason at all.
But if they want to create a custom background, then there has to a reason for that custom background at my table. Because otherwise, it would just be a default of, "Pick two skills, pick two proficiencies/languages, pick one feature." And that's not how we roll.
You can roll as you wish, preferably without insinuating that we are engaged in playershaming and #badwrongfunning people.