Hi there, good question! Some year ago, I made a self-test with SCSS and frameworks, just to test and see the world from another perspective (after all, SCSS is also used a lot by Harry Roberts).
After working with it on one project, I returned to my all-time fav. combination: VanillaCSS + HTML5Boilerplate normalization. Yes, the frameworks do a lot of stuff which tried to make my life easier, but they disrupted how I work. I want to use BEMIT and ITCSS and at the same time deliver very small CSS. Something like that is not quite possible with these frameworks, so I stay with VanillaCSS.