In most developed countries cash is too inconvenient for regular people to bother with it anymore except when they have to - it is just simpler to pay for things digitally or with a card. But even “free” governments already have total surveillance over digital transactions. So as the remaining legitimate uses (and users, since I think most regular people who would be legitimately harmed by going cashless are very very elderly people who would struggle to adapt) for cash die off pretty much the only remaining reason to use cash is to commit crime - the vast majority of which is tax fraud, which effectively harms every citizen who isn’t committing tax fraud.

Basically, eventually cash will basically become the “crime mode” for its respective currency. I don’t see why it makes sense to continue to allow cash at that point. FWIW I do think privacy for transactions is important but I think we should be trying to make digital transactions more private rather than clinging to a mostly obsolete (in 20 years will anyone be unbanked or transacting in places with no internet?) technology.