It still is, surprisingly often. It pops up whenever the cable length has to be longer than 100 meters (too long for copper Ethernet) and has to be cheap (so fibre transceivers are out). In the large-acreage world of solar farms, this happens pretty often.
RS-232 is also weirdly still popular in and between electrical substations, and the 25 m range limitation is overcome by a copper-to-fibre serial converter at each end. For long haul data transmission, the fibre is often optical ground wires - fibre optic cores wrapped in steel cable that runs along the top of high voltage transmission pylons. Why don’t they use fibre optic Ethernet for long haul data? Because a) they’ve got a lot of legacy devices and the new devices are backward compatible, and b) the cybersecurity is hard to beat. If you hack into the serial link, you only get access to the endpoint box; you can’t use it as a “jump box” into the remote network.
