You need to do the accounts to see it (profit and loss / balance sheet for each stakeholder). A miner only makes a small profit because most of the revenue they receive from the sale of their mined stock is passed on to the blockchain and serves to increase scarcity. The miner's balance sheet grows very slowly because while the sale revenue is passed to the blockchain, the capital acquired (travelling in the other direction) is passed on to the secondary market buyer.

The profit the miner makes is what grows their balance sheet and that may only be 5%-10% of the capital flows that pass through their hands if they're lucky. This "profit" is the capital lost to the ecosystem in brokering expenses effectively.

The accounts for the masternode however are different. The masternode's balance sheet will grow at a far faster rate since the revenue obtained from exchange sales goes straight onto the masternode's balance sheet and stops there. It does not get passed on to the blockchain and does not contribute to "scarcity" (by way of increasing difficulty). This "profit" is also capital lost to the ecosystem just as with the miner's profits, except it's far greater, in fact the full market value of the coin

So if you look at from an outside investor's point of view in terms of what's "backing" the supply it looks like this:

In fully mined POW the whole supply is "backed" by the marginal cost of mining. In Dash only half of the supply is backed by the marginal cost of mining, the other half of the invested capital ends up on masternode balance sheets which ostensibly "back" that part of the supply. But of course that's useless to an investor since any realisation of that balance sheet capital (MN selling rewards) only serves to deplete the capital value of their own holdings. They're investing in the masternode's balance sheet, not blockchain difficulty.