Is grid uncommon?

After finishing the Responsive Web Design projects i realized i totally overlooked the Grid technique. I dont recall it being utilized in the projects examples, while flexbox was well utilized. I adopted flexbox in my own projects and grew used to it, but i stuck with some flaws to that design.
Why is grid not promoted more in the RWD projects and is it generally less used technique compared to flex and if so, is there any reason for that?

the project examples are just an example, you don’t need to do projects exactly like that.
you could redo all projects using grid to learn it.