Marketing reasons aside, I don't really object to having 16:9 be the base ratio that other ratios are compared to by changing one of the numbers (instead of doing the maths and dividing both sides as much as possible), taking into consideration that it's the default screen ratio for far and away most of the screens in the world right now.

"This screen is 16:9" -> oh, it's a normal screen, aka widescreen

"This screen is 21:9" -> oh, it's one of those weird cinema screens that are wider than widescreen
"This screen is 7:3" -> uh, it's wide, but where's my frame of reference?

Or how about the slightly more exotic:

"This screen is 16:10" -> oh, it's slightly taller (or wider) than a normal screen
"This screen is 8:5" -> ???

"This screen is 16:12" or "this screen is 12:9" sounds silly because the idea of '4:3' is clear enough by itself, but in general, 16:9 is a useful point of reference.