If you lose on average $4 per trade, opening and closing because of PFOF, multiply by 250 days of 200 transactions per day deduced from your calculation, you lose $200K a year. Is that difficult to understand? Sure you save $2.50 per transaction so your net loss is still $75,000 a year. That $75,000 is your lost profit, profit that should've been in your pocket but instead went to the MM's pocket. Think about it. If the MM's losing money on every single trade even after paying for the order flow, how can they still be around? They would've been bankrupt long time ago. WHERE does their profit come from? They keep saying they pay to the broker for the orderflow and then they give us price improvement so how do they make profit? Where is their profit coming from? Remember they are MM's. They are not long-term investors. They make two-way market so that means as soon as they buy or sell from one party they flip it simultaneously or quickly afterwards. So if they gave us a good price, a price supposedly better than the market price, how are they going to flip it higher(lower) when the spread is so tight? And remember they still have to cover the orderflow payment cost that they paid to the broker and everything else.
I personally use both PFOF brokers and non-PFOF (supposedly) brokers and I can tell you from my personal experience my orders get filled faster and at better prices with non-PFOF (supposedly) brokers. All of the PFOF MM's have been asked to provide more transparency about their business model. So far, all of them refused. You wonder why. If they are giving us so much price improvement, why are they so reluctant to show us?