Bright dust shouldn’t be a currency to buy tributes in the tribute hall. It’s an in game currency which can be bought with real money, which could encourage spending of real money to complete the tribute hall. This could be an oversight on Bungie’s behalf however it shouldn’t be used here, it’s a vanity item/ eververse currency. Not to mention it’s quite difficult to farm in large quantities required to buy the tributes.
How is it bought with real money? You can also earn bright dust by just playing and doing eververse bounties, and once your discount is 80% it’ll cost almost nothing.