Good question...this is where it gets a little confusing. There is a dev fee (2.5%) for using the OS and a pool fee (2%) for using the pool. When you stay within the Braiins Pool/OS ecosystem, they only drop the pool fee. With a bitmain miner, you have to use an aftermarket OS or you loose up to 20% efficiency gains. By waiving their pool fee, Braiins is pulling more people into their pool. More people = more blocks = more consistent block rewards
