It's currency independent. Instead of having to provide a different price for each country/currency, you can just say it's a certain number of credits and simplify the look of your store for it. That's one reason why it's common in virtual stores in games (it is still a dark pattern and can be used to take advantage of people, I agree, but it also has its benefits).

Everyone around the world can discuss an item and be like 'it costs 50 tokens for blah' and do comparisons between items in the store based on simple token amounts, but actually be paying different costs (and see different amounts) for it with their own currency.

To use programmer terms, it adds a layer of abstraction on top of the service, with all the associated pros and cons that goes along with that.

It does allow you more flexibility with pricing. As an example, iStock sell photos that cost 1 credit or 3 credits depending on how fancy they are. But the credits cost a variable amount depending on whether you bought a few credits or hundreds. So they can offer a tiered a la carte pricing structure that also has bulk discounts. Hard to tick all those boxes without credits.