You laugh now, but at least you could turn the dialogue up over the music by adjusting the balance. I’d almost take this over not being able to hear a damn thing anyone is saying in modern TV audio.
Check if your TV is playing the surround track. Modern TVs are hell-bent on serving you the multi channel audio, regardless of it's being played through the built in stereo only speakers.
Surround is mixed for high dynamic, talking is 'talking volume' and loud shit is indeed loud. In contrast stereo is pretty much normalized, so you can here everything at moderate volume.
Is mostly because stereo sound being widely available was novel and new. I have several albums that are literally just made to let people show off the stereo aspect of their new hi-fi.
And there are some old mixes that are fairly extreme by today's standards but sound like a very real soundstage - the drums are over there, the vocals over here, etc.
But then some took it too far with the control hard pans and then relying on the hard pan to fix bad levels (like that the drums are too loud)
But even today, it's not unusual to have some instruments entirely (or very nearly) in one side of the other. Just not the primary instruments carrying the harmony and melody.
Trivia: the Beatles only sat in on the mono mixes of their songs because that's what'd be on the radio. The stereo mixes were done by the producer and the sound engineer without any input from the band.
When done effectively, it does sound awesome that way. My buddy and I (both making music) talk quite a bit about strategic use of similar techniques but subtler when we mix music today.
So part of it was to be backwards compatible with some mono record players, that might be the needle explanation. Another part was how the mixer wanted to use the two channels. Are the channels left and right, or two mono channels of vocals and instrumentals. Lastly it was because mixers could do that when just a short time before they couldn't. They were artists who were experimenting with a new medium. It wasn't just one reason, and it wasn't for very long really. It's just a lot of music was recorded during that time.
I've a few "learn the violin" CDs like that. Solo instrument on one channel, band/orchestra on the other. As you get better at playing it, change the balance.
Not so essential for classical music, since music notation pretty much marks exactly what you should play, but great for folk or jazz when there's a lot of "unwritten" style knowledge that you need to learn.