what's so unusual? it's easy to understand

first it was 4:3, then (4:3)^2 = 16:9 and also 16:10 (also it has to do with old resolutions like 320*200 (16:10), 320*240, 640*480, 800*600)
then from 16:9 it evolved to 18:9

when you say 2:1 you have to calculate to understand how it is different to 16:9, whereas 18:9 tells you which dimension became bigger comparing to usual ratio.

PS 3:2 is nasty to look at, would be better if it was called 15:10