There's lots of reasons. None of which favour the consumer, all of which favour the retailer. The bar staff stealing is a factor, but a minor one in the grand scheme of things.
The name a few:
psychologically the customer will spend more - because handing over paper tokens doesn't have the same effect as handing over hard cash. Bit like monopoly money!
profit margins will be increased - dozens, maybe even hundreds (thousands?) of customer will buy tokens that will ultimately get unused. Lots of events won't even exchange back surplus tokens, so they are lost into the mire. And how many will go home with tokens still in their pockets/bags.
Also - from a security point of view - makes sense to only have a few points where cash (and a lot of cash at that!) is being collected and ferried from/to.
Some friends where there and said ushuaia was different from how it was a month ago when we all went; kids dropping rubbish everywhere, pushing and general idiot behaviour. I've never been in August, it always like that or just special events like this?
It'd a shame about the litter thing. Although I have noticed how full the bins get after like midnight. Also if you try and do the right thing and pick a bottle off the floor and put it on a table expect waitress to go mental because you didn't buy it there. wtf. (Bar along sunset strip...)
The thing about kids thinking is good to act like idiots and get completely wasted; I've actually talked to some in the past and basically they're doing it to fit in. One even said they wish they didn't have to drink lol.
One day they may actually get what Ibiza is about