> why the fuck are you bothering me with this?

Handling cash is a hassle in many ways:

1. It's slow. Obviously it is not slow in the best case when the customer throws in the exact change, but it is _really_ slow in the probably more typical case when the drunkard is at the counter and starts to dig into the pockets and find out if he has enough coins or when the seventh customer in the row wants to pay his ten cent lollipop with a hundred dollar bill and you run out of change.

2. It ties capital to keep sufficient amount of change in all of the booths.

3. It is difficult/expensive to manage securely and safely. You need to figure out how to stop personnel and other people stealing the money. Also your personnel likely feels more safe when they know that nobody can think that hey can come and try to steal money from you because you simply have none.

It's only slow because you are not used to paying with cash. Most payments are done with cash here, and the few people paying with cards cause small but noticeable delays. Counting cash is usually faster than handling a card reader, entering the PIN and whatnot. The odd drunkard or elderly customer is comparable to the odd technical problem, which usually takes longer to resolve.

I think it is also slow because the US does not require prices to be displayed including sales tax. If you pick something that has a marked price of $1, the total price will be somewhere between $1 and $1.10, depending on which state/city you are in, and what category of goods you are buying. Unless you are familiar with the exact tax code of your area, you won't be ready with exact change when paying. Even if you are, it means that you need to manage all the worthless pennies and nickels that result from paying with cash.

How is that faster than slapping my contactless card to the side of the card reader? 1 second and back to my wallet it goes.

Or if I'm feeling extra tech-y, I can do that with my watch or phone.

Where on earth do you live where things are this backwards?

1. Just don't accept any bill over €50 (this is common in shops too, no one expects to be paid for groceries or a beer at a festival in €100 bills). Most people are still pretty skilled in handling cash, although this is a declining skill. We've been doing cash transactions for centuries, we're still pretty good at it. The occasional slow-down is more than made up for by not having to charge or top-up your bracelet or what have you (you come prepared to the festival with cash).

2. A negligible amount for a vendor on a festival.

3. Not a problem on a festival. Booths tend to be manned by two persons because of other safety factors anyway, so staff stealing isn't an issue, and any organised criminality on a festival is usually limited to (relatively) low risk, high reward crime: pick-pocketing (smartphones in particular).

Oh, I agree it is a hassle for the merchant, but the fact that they’re making things more difficult for their customers remains the same.

And especially the ‘takes longer’ argument just shifts the time people are waiting to the charging station, or to their own homes, if they’re charging beforehand.

I think it’s fairly easy to make any change handling easy by making everything cost multiples of $1

also known as f-the-customer.

so use MasterCard/visa?

To add to that: because we all know that both parties know a working money system exists, then the most likely explanation for "why" becomes "because it is profitable for the festival host." The festival goer is tight to be naturally skeptical of sny alternative payment system (smart wristbands, "credit" cards, tickets/tokens).

Even if some transactions have extra friction such as ID checks for age-restricted purchases, the less intrusive solution is color coded "dumb paper" wristbands.

I suspect this allows the festival organizers to more easily take a cut from the merchants.

  have zero insight into how much I’ve already spent 

Maybe that's a key motivator?