I think that @JLoon hit the hammer on the head…., figuratively.
Erotic stimulation.
I remember when I was, maybe fourteen, I was on a playground, around dusk, when suddenly, in the corner of my eye I saw a woman, through the window, in, what I assumed was, her bedroom, changing from day cloths into evening gown.
Man…., I came back days in a row, around the same time, but I never saw her again.
So, I was a creep, a peeping Tom.
Without knowing what that was.
But yeah, it was mesmerising, I can’t lie.
Another thing: both men and women like voyeurism and/or exhibitionism.
Take couples that engage in mutual masturbation, for example.
Watch and be watched.