Think about it this way. If Lycett had said, “David Beckham, please rethink your deal to promote the Qatar World Cup otherwise this money is going to charity, then there’s no way that Beckham could’ve changed his mind about the deal. He’d be effectively saying, “Okay Joe...please don’t give that money to charity - I’ve pulled out”.
Anyway legally there was nothing Beckham could’ve done at this late stage without being in breach of contract. He simply couldn’t walk away from a deal that would been struck months ago. He would be sued for millions.
Burning the £10k is a more effective protest than giving it to charity.
Same as the KLF stunt in 1994. People still remember that to this day!