Because game designers in the 80s and 90s had the ability to try things out and release something without losing money on a massive scale and they also didn't have to fear causing a massive shitstorm that would forever destroy their reputation.
Most of that stuff is basically: "baby did his first game"
If you had to design a Lego set instruction handbook right now, I'm pretty sure there would be plenty of people who couldn't work with what you came up with and couldn't finish the Lego set they bought and would have to finish it on their own somehow.
Stuff like that takes time to develop properly. Not everything they think is good/fun turns out to be good and fun. Something they consider intuitive might actually be the opposite.