For a long time, simple things like vertically centering dynamic text were impossible to do except with JavaScript or weird hacks. Or how do you push a page footer to the bottom of the viewport on pages where the content is only a few lines? Or create a two-column layout where the left column has a different background color that always stretches to the bottom of the viewport?

There have always been a ton of common, simple things that CSS just didn't support, or required bizarre hacks for -- like reusing "floats" intended for inset images as the basis for layout. Over the years it's gotten better, but if you've been doing this for 15+ years, surely you remember the old horrors. I don't want to have to insert "clear: both;" at the start of every new section ever again...

Not to mention that back in the day, browsers weren't nearly as standards-compliant, so your designs would just show up wrong in some browsers, and you'd rip your hair out trying to write CSS that would work in all of them.