I would have to respectfully disagree; every grow I've worked for has used synthetic nutrients and flushing has nothing to do with whether tests are passing or failing (I've been told by several facilities you have to work pretty hard to fail for heavy metals; but the first grow I worked at sure as shit failed for cadmium of all things, but he also chose to not run certain membranes on his RO system and the source water was incredibly sketchy with heavy metals (I know a shit ton about our local water supply out here.) First thing he did was call up Jack's Nutrients and told them their 3-part formula caused his grow to fail for cadmium, they said "bullshit, lots of grows use our nutrients in Colorado and never fail."
Not a single commercial grow could explain why they flush, other than "a consultant told us" or the best (and most plausible one) I've heard was "it saves us 2 weeks worth of not spending money on nutrients," and that's probably one of the best reasons right there.
Commercial growers are just home growers that are growing in scale. There isn't anything specifically magical about it, a lot of the same products we use at home are used in commercial growing. And a lot of the bro science from home growing is just STEEPED in the commercial side, because these are the same guys like you and me that have been piecing together scraps of info for decades trying to figure out what's what.
That's the internet brother. You will NEVER not have that way of thinking; but it's in places like this that we try to promote the civil discussion of said topics so we can try to get to a "generally agreed on" consensus. That's the beauty of a peer-based community, we get the collective knowledge of thousands of people. And when we can use science to back up that knowledge and everyone goes "ah yeah, this DOES make sense," that's how we start making changes in the way people think about things.