I got no digital sound out of my 4k blu ray player via optical. I did get sound via optical from TV (via HDMI from player to TV) but now I am getting horrible digital noise instead of disc audio. I feel like giving up!
Check setting menu in TV - it probably has an optical out audio mode selector somewhere.
As for why so many different connections, well they all came to be a long time ago to serve different physical and/or signalling purposes at the time. While some of them in the early days may have been derived from each other at a signalling level (and later made signal compatible), they may have been designed to serve a different purpose at the physical level (balanced AES vs unbalanced coax SPDIF for eg - AES is used in the professional world where 24 bit over long cable runs was needed vs the 16 bit SPDIF of the time). In some case, same connector may be used, but the underlying signalling is different - stereo TosLink vs 8 channel ADAT for eg.
HDMI is a different thing again to fulfill the needs of digital video which also needs to carry multi-channel audio and these days in both directions include compressed and uncompressed formats at various sample rates as technology has improved on the years. Like other mechanisms, that has evolved a lot over the years as well to support higher bandwidth (resolution), device control, audio return from TV etc.
These days add USB 2 as well because that provides the means for full control of a device from computers as well as much higher sample rates and bit depths.
IIS was only ever intended to to be for on-board communication between a microcontroller and a DAC chip, but because it offered a clocking advantage over SPDIF, then people decided it could be useful for feeding audio data into a DAC from outside the device, so some devices ended up with IIS connectors (of which there are many as there is/was no standard for this).
Over the years some of the earlier and similar signalling has been unified (SPDIF, TosLink and AES), but still they want to keep connectivity with existing devices.