I can see why they did it. Now that screens are ~universally 16:9, vertical space is at a premium. It would be nice if the hamburger menu actually replicated the same functionality though.
I think that if vertical space were indeed the reason, then we wouldn't have huge, touch-sized widgets everywhere and 32-pixel titlebars. There are applications where simply reducing the padding on most widgets to sane values wins you 3-4 menubars' worth of space.
I'm sure vertical space is the most often-repeated argument, but I'm skeptical that it's indeed the reason behind this trend.
16:9 is a ratio whereas the amount of vertical space is an absolute amount. I don't think the two are related, unless screens got wider at the expense of height, which surely is not the case.
They did lose height; 1600×1200 → 1920×1080. For a while you could find 1920×1200 if you looked hard and spent more, but at the next increment everything is 16:9.
I have 2 1920x1200 and there is no reasonable upgrade except maybe something like 40" 4K (and not in retina/high dpi mode). 2560x1600 would be ok, but it's too expensive.
3440x1440. Less pixels overall than your current setup, but incredibly nice to use. Also affordable, you can get them for under $400 during sales / end of year clearance.
Seriously, for coding I absolutely love a 1920x1080 screen rotated 90°. Still wide enough to see an entire (sane) line, but more vertical space is just wonderful. Can't watch video, obviously, but for a work computer the vertical space is the absolute best. Improves web browsing as well for most sites.
I tried a 36", I can't stand it as a display. Fine for a TV, but it's a little much for a monitor. Although I can't stand more than 2 displays, so YMMV.
They did get wider at the expense of height. Monitors are sold by diagonal size, and a 15" 4:3 monitor is 9 inches tall while a 15" 16:9 one is only 7.4" tall.
