However, given that international travel took a nosedive in the last 18 months whilst banknote production continued to stampede, I'd have to suggest that hoarding by globetrotters doesn't account for any current discrepancy in production vs use in observable trade.
It's three times what I routinely carry, which is still above average:
https://www.bloomberg.com/toaster/v2/charts/892967a8146e4cc8... or https://www.statista.com/statistics/787626/average-amount-of...
Regarding cash to carry, I basically am not concerned with pick pocket / theft, for a number of reasons, and am more concerned with a business being unable to take a card for some reason. For instance, my primary travel card is an American Express which is not accepted by small businesses in a lot of countries, such as restaurants and shops. In these cases I have a backup card, but I would prefer to use cash. I also ensure I have enough cash to always get me back home and in communication, so enough to replace my phone and get a return plane ticket.
I imagine locals don't need to carry as much cash as foreigners because they have a different set of concerns and easy / ready access to more cash without being charged exorbitant fees for access.
I have a single debit card, and a credit card I haven't used for years (I always failed to pay it off at the end of the month). The reason I carry cash is in case my debit card stops working - suspended by the bank due to suspected fraud, card stops working in card-readers, bank decides to close my account without warning or explanation.
£100 should last me a couple of days, in which time (hopefully) any problem with the card should be resolvable.
I don't carry shrapnel any more. I don't use cash in shops, unless they have a minimum card spend (then I have to carry the shrapnel change home). COVID has led to many shops having a preference for card payment, so I comply.
Perhaps I should peel off all but £30, and keep it somewhere safe at home. But I'm not afraid of being robbed in the street.
Between food and drink, lunch, busfare etc $100 generally covered most expenses beyond tickets to events, and then $200 USD was usually enough to solve any significant problems if you miss your bus ride home or whatever. If you sprain your ankle in some castle ruins, you likely don't want to spend half the afternoon hobbling around historic cobblestone roads in a village somewhere looking for an ATM to get taxi fare back to the hotel. Taxi drivers rarely turn down USD.
That said, ATM fees internationally, depending on your card issuer, can be pretty expensive, ATM fees + forex fees can amount to over 10% if you're only pulling out $100/day. If you don't mind the risk, pulling out the maximum amount of cash per day (usually $400 I've noticed) gets total fees down to about 4%. If you're a student backpacker on a budget for weeks on end these fees can be a substantial fraction of your travel savings/budget.
I don't carry less than the cost of a new phone, new laptop, and at least a week in a hotel.
All sorts of systems can fail that make cards and ATMs stop working. Look at Puerto Rico after Maria.