Yeah, being able to open the window just slightly from a different angle doesn’t seem like that useful of a feature. Also in the US we mostly have a different style of window (see below).
It’s rare that I want to open a window, but only slightly open it. Normally it’s all the way open and I probably put box fan in the window to pull air through.
You’re correct that many houses these days are built too air tight, but for older houses that were built before AC the house was often designed so that you could open windows on different sides of the house to create a cross breeze. So for example, you could open up windows on the East and West side in the morning and the temperature difference should create a convection breeze through the house.
So what if they didn’t use a proper ERV setup?