The 16:9 screens. Once upon a time they were called widescreens because many people were used to small (in inches) CRTs or LCDs (even with square panels.) Basically they were 12:9 and those 4 extra units on the horizontal axis become real extra space. Unfortunately most people only got 768p screens on their laptops while all TV sets had 1080p and some of the old monitors were 1024p or 1200p. So "less vertical space". And then when you have a 13" laptop you don't have much vertical space no matter the resolution.

We're talking about things like dialog windows that don't take much vertical space even when putting all confirmation buttons in separate rows; this is a set of applications that often easily fit on half the screen. I know what you're talking about, I'm writing this on a laptop with 13" screen and I'm using a browser with vertical tab bar for a reason, but this isn't that case.