It's not just that women reading this flyer wouldn't be interested in showing up, it's that they are instantly reminded of how the programming world perceives them and their place in the industry. It reminds them of the sexism they've endured their entire professional careers and it reminds them of how little has changed.
"Lots of hot men serving beers" isn't a very comparable example because male programmers haven't been discriminated against (at least, not professionally). A better example would be if the flyer were changed to "lots of Mexicans serving beers" or "lots of African Americans serving beers". Wouldn't that offend you even if you were able to somehow derive how the marketing people arrived at this approach?
"Lots of hot men serving beers" isn't a very comparable example because male programmers haven't been discriminated against (at least, not professionally). A better example would be if the flyer were changed to "lots of Mexicans serving beers" or "lots of African Americans serving beers". Wouldn't that offend you even if you were able to somehow derive how the marketing people arrived at this approach?