If you were in the Olympics what price would you accept to be slightly nobbled? I don't know what Swatch is paying beach volleyballers to wear there watches but I'm guessing it is relatively substantial.
I've played a lot of beach volleyball and I don't think I've ever seen anyone wear a watch. The ball hits your wrist a lot so wearing a watch is kind of off-putting. Apart from money there can be no real reason why you would do it. Really, you have trained for four years for this moment - you are not going to be checking the time to see whether you can meet up with Gary for some beers or get home for mum's lamb roast.
I'm guessing lots of beach volleyballers have taken Swatch up on their offer because the normally get paid shit money. It must be really embarrassing holding up an oversized novelty winners cheque with $3000 written on it when you have spent twice the amount on airfares.
Good thinking by Swatch though - lots of super-slow-mos proudly featuring the product wrapped around tall, athletic, hot people.