The standards were also a lot lower back then. Modern-day users expect high resolution and color depth for their screens, seamless hardware support no matter what they plug into the machine, i18n with incredibly complex text rendering rather than a fixed size 80x25 text mode with 256 selectable characters, etc. These things take some overhead. We can improve on existing systems (there's no real reason for web browsers to be as complex as they are, a lot of it is pure bells and whistles) but some of that complexity will be there.