Maybe one day we can eat this protein directly. But the issue is the taste and "ick" factor. We can barely get people to eat a vegan diet, or insects, let alone raw protein sludge. This kind of protein does have the potential to be mixed in other food as supplements, like with flour, protein powder or protein bars.

Well, is the objective to feed people, or to feed people high quality fish? Food isn't a fungible commodity, and the fact people simply like meat more is enough to justify the costs, both to the people buying it, and the people making it.