Formal standards aren't essential for interoperability.
"Essential" is interesting because you could definitely argue that HTTP isn't essential, but I don't think there is any feasible way of denying that the formalization and acceptance of early internet protocols (UDP, TCP, HTTP, FTP, etc) have played a significant role in shaping our modern technology world.
In a similar way, having reasonable standards makes it easier for everyone that isn't an expert in a particular field to just use something that is likely to work reasonably well while they worry about some other special part of their idea.