[sofixa]

I think you might be comparing different things and making the wrong conclusion. Before "the modern era and Internet" there was much more place on airplanes' seats. Squeezing every millimetre of space is a new(-ish, it's been what, 10-15 years now) trend born out of low cost competitors doing that and severely undercutting legacy carriers, who replicate. So if everyone reclined 30 years ago, it still probably resulted in more space available for everyone compared to today, even in a non-reclined configuration.