This is price discrimination. Everybody would love to charge more money to rich people and less money to poor people, since that increases the total profit.
The only companies that we directly allow to do this are schools, but having a premium version lets you approximate this.
That's because you usually pay via credit card (or some other financial mean) which is cumbersome (and may be illegal) to spoof. But yeah, it can be hard to justify a subscription when it's the price of a full meal. Especially when other essential subscriptions (electricity, water, internet, cell services,...) is straining your monthly budget.
Steam also does this. Most games are significantly cheaper in low-income countries like mine because otherwise they wouldn't make a dime here.