If you're incapable of reaching above your social level, but hard work will improve your economic status, then looking like a hard worker will be hot.

Women throughout any given society have often crippled, poisoned, abused, and starved themselves in order to attain certain looks, though. No matter their social status. Even when it meant they literally could not do the labor that was necessary to keep their families at the same economic level.

The thing about Tsarist Russia is interesting, and I wonder if the fact that the gap between the nobility and the serfs was so incredibly huge had something to do with it. Though there have been, and are, huge gaps between social class while the lowest women on the rung attempt to emulate the highest plenty (and are shamed and considered unmarriageable if they don't).