Stake makes its money in three ways.
Brokerage Pack fees associated with Stake Unlimited and Stake Black (from July 1, 2020)
The FX fee and associated fees (e.g. Express Funding) when you transfer $ into and out of USD
Interest earned on cash sitting in the US brokerage accounts.
Up to two trades per month within Stake Starter and every single trade within Stake Unlimited and Stake Black are offered commission free.