At industrial scale, surely they recover that copper from the etching fluid?

Even if they do, the recovery itself would surely have costs. It can't be easy.

Indeed, the enchant is very nasty stuff, it's not easy or clean to do so.

Yes, but this costs pales in the cost of redoing in case of problems with side-etching and the overall tightened manufacturing constraints.

And yes, they get to recover the copper, at the very least to make treatment easier for discarding (copper is a very bad pollutant). But not only there's a cost, this is dealt with by waste treatment companies that will at most use the copper value to recoup some of the cost of the treatment.