I guess that's pretty common, stiletto heels are all over the place when it comes to pictures of hogtied women, or girls standing with arms stretched taut overhead, so that both shoes and feet become very prominent.

In one sense high heeled pumps or boots are a sign of the feminine, in another way I feel the high shoes and luxurious attire of many bound women in pictures are there to show up luxury, to signal "here's a woman who lives in a luxurious world and is able to get anything she wants, but she's been bound, gagged and fucked like a dirty slut". There's a contrast here, either she wants to go into that part, to be bound, used, punished and made a slave, or else she's been overpowered in spite of her wealth (the classic "damsel in distress" thing).