It's way more complicated than that. Bear in mind many of the network protocols in use today are decades old and have been constantly evolving, but there has generally been a consideration to maintain interoperability.

Then consider that not all vendors implement the standards identically, because the standards can be a bit woolly and in some cases followed rather than lead live implementations.

There will be a bunch of code that looks useless, but is actually there because of specific interoperability scenarios.