Maybe I’m missing something but shouldn’t something like this armoured fibre be fine to run inside your walls?

I’m really confused by the number of people here that are conflating Ethernet as a protocol and the physical medium it runs over. Coxial, fiber, and twisted pairs, can all carry different protocols. None of them are as ubiquitous in the home as Ethernet. Alternative network technologies are usually specific purpose, like fibre channel for storage, or infiniband for low latency, or 5G for wireless telecommunications.
It’s a very long lived protocol and it’s a testament to its lightweight and flexible nature. Ethernet really is a framework for higher level protocols where increasing change happens. IP addresses? Not Ethernet, that’s all Internet protocol. It’s more reminiscent of when electricity in the home was becoming common place. Before standardisation there was all kinds of chaos with different sockets, voltage, AC vs. DC etc. Although arguably that’s a less settled debate with suppliers and home users often preferring different standards.