Unfortunately, though, just using a CAN or Ethernet physical layer doesn't solve the problem of the https://xkcd.com/927/ standards proliferation of industrial protocols: Some customers require CIP motion over Ethernet/IP (a dog-slow Rockwell proprietary protocol), there's old MACRO fiber optic rings, Sercos III (and prior serial protocols), a dozen high-speed serial standards for communicating with absolute encoders, and, of course, good old-fashioned hardwired digital I/O - which might be either analog velocity/torque or step and direction, RS422 differential or single-ended, etc. etc. etc.
You'd hope that you could just plug something that spoke CAN or Ethernet into something else that has the same physical interface, and the two would work together. Sometimes, you get lucky and that works out. But the ever-forward march of industry leaves behind a graveyard of yesteryear's abandoned products and protocols.