The problem isn't the number of bins, it's that only so many people can be standing next to them at any one point. Traffic flow is shit at the best of times in crowded places - imagine how worse it would be if everybody went to find a bin every time they needed one!
Joking aside, it looks bad, but it should have been anticipated. Agreed with the above points, it should be between the organisers and authorities to sort - and the sooner after (or better still during) the event, the better.
Swear people wait especially for the aftermath of events especially to take these photos. Easy to take a photo. Easier still to pick up some rubbish and dump it in a bin. No, it shouldn't be the responsibility of innocent bystanders. But if it bothers people that much, it's not much effort to chip in. (See the various beach clean-ups that take place here and elsewhere, which whilst are for the greater good, it could be argued that they're counter-intuitive).
Just to point out, I was that cool guy who carried a carrier bag throughout, and disposed of it sensibly after the crowds dispersed!
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Unfortunately, you can't have amazing public events
and litter-free streets. There does need to be an effective clean-up operation plan in place. But if you installed more bins, then that's less space for people, and the crowded zone would just take up a larger area and be pushed further backwards.
No number of bins could prevent this, unless there were so many they'd be no space for any people!