Well you can still make websites with plain HTML and CSS today, and the layout modes (and other niceties like border-radius) that are available today so are much nicer than the ones that were available 20 years AND they work the same in every browser!

20 years ago you were cobbling together layout with tables and floats (you didn't even have `display: inline-block`). And people still wanted vaguely responsive layouts even though there weren't any media queries yet. Plus there were 3-4 major browser engines that you needed to test with, and there were often major differences in both feature support, bugs and layout between them. For example you had to deal with the fact that IE used what is now known as `box-sizing: border-box` while other browsers used `box-sizing: content-box`, and the fact that browsers didn't even parse HTML consistently you could easily end up with different node tree in different browsers.