1. there's a trade-off between graphics/sound quality and story complexity. The better quality your voiced dialogue is - the more you have to pay for every additional line - so you tend to shorten it. Same with graphics - it's one thing to paint 8 frames of 32x32 sprites. It's another to motion-capture, model, texture, and process 100s of different versions of each character animations.

2. you're comparing unfairly (looking at the most complex examples from the past and comparing them to modern average). There were LOTS of very simplistic games in the past. You just don't think about most of them. Some genres went extinct because of how simplistic they were (see the dungeon crawlers where there was no dialogue or story whatsoever - just moving at 90 degree and hitting monsters) - it's the "old music was better" fallacy - you don't remember the old music that sucked.

If you compare most complex modern games they blow out of the water anything from the past. Let's say Baldur's Gate 3 or Dwarf Fortress or Minecraft compared to let's say Elite or Betrayal at Krondor.