Playing devil's advocate, that strategy can still end up with a deficit of women. If your selection bias is (pretty ^ young) women > dudes > (unattractive v old) women, your hires are still going to be predominantly dudes, unless the talent pool is so deep there is always a qualified woman available who is also pretty and young .
You have a good point here, but just from what I've seen with symphonies, it seems like usually the performers, of both sexes, are fairly young(-ish). And they're usually all reasonably attractive. They're up on a stage for people to see them, after all, so naturally whoever's trying to keep ticket sales up is going to want them to look nice.
