1) There is a societal and cultural problem with the way that nudity is treated. Nudity is often seen as inherently sexualized, and public nudity is considered by many to be part and parcel of some sort of sexual deviance. (I should note that while it is not illegal for women to be topless in public here, that it is nevertheless monitored and discouraged by both law enforcement and the public at large.)
2) There are demands (perceived or actual) on bodies that are revealed on public beaches which are mindblowingly hostile. You’ve heard it before, the snarking about which girl looks fat in her bikini, or the friend that REFUSES to buy a bathing suit because she’s terrified about being judged for her appearance.
3) There are pressures put on aging bodies to cover up, to be extremely modest, and not to reveal loose flesh and wrinkles to the world (especially not on a beach). (In fact, a recent photography project that used older women as pin-up models reveals, in some of the comments received, ongoing prejudice against the aesthetics of the aging body.)
4) There are pressures put on male bodies to conform to a series of aesthetic principles (muscles, little to no chest hair, abs, etc), and these are increasing with each year. I know many men, of various ages, that struggle to feel as though their bodies have worth, as though they are lovely and perfect just as they are.