Flexbox is still fairly new! Hmm, maybe I'm just old.
While a lot of devs love to use brand-new stuff that's only just been added to some browsers, some of us are not willing when we know it won't work for (almost) all users. The scroll() function is too new for use in production, IMO (but good to know it exists, to revisit after a while). If I have to code something else anyway, or copy-and-paste a polyfill, then why not just use a more robust option in the first place.
While a lot of devs love to use brand-new stuff that's only just been added to some browsers, some of us are not willing when we know it won't work for (almost) all users. The scroll() function is too new for use in production, IMO (but good to know it exists, to revisit after a while). If I have to code something else anyway, or copy-and-paste a polyfill, then why not just use a more robust option in the first place.