Back again to ask why having sand beneath your shoes makes such a difference? I understand concerns about weather and heat, but those concerns apply to all those summer outdoor weddings in the US on converted farms. And no one is up in arms about that. Here you may actually have a cooling sea breeze and don't have to stare at cliched "vintage" barns and shiplap everything in 85 and 90% humidity at 10pm in Tennesee.
@Kurps comment is not beach specific and is what everyone thinks about all of us when they see us in a blazer and leather shoes when they're in sweatpants and sneakers...
@lax101 is probbaly right that this is mainly to keep the three button open linen shirts to a minimum. And I think its a better option than saying "Suit and Tie. And we mean it."