Nearly all TVs have an SPDIF out and can send 5.1 Dolby Digital extracted from whatever input (Streaming, Blu-ray via HDMI, broadcast, etc.) to that output. I’m sure you’re 20 year old receiver already had an SPDIF input and a Dolby Digital decoder.

You could have easily kept that setup with the same level of soundquality the whole time - assuming nothing breaks.

I think large 5.1 just went out of fashion due to the size and cable requirements and the fact that soundbars became good enough.