My Mistress is a Masturbaterix. She loves cocks. More specifically, she adores making them cum.
Partly this is because she loves the fact that she can- not every woman has her technique for wanking men to orgasm- often it's too hard, too gentle, too fast, too slow; in her case she has an expert grip, an innate understanding of how cocks work. But fundamentally, it doesn't matter, since she is TAKING the orgasm rather than giving one, and in that context, it doesn't matter how satisfactory her technique- you WILL give her the orgasm she desires, however painful and premature or delayed that might be.
Partly it is because she loves the animal pleasure of it, especially if she is combining it with another stimulus, notably pain. I have seen her brutally jerk men off with a powerful arm across their windpipe, specifically to see how their body reacts to the conflict she brings it.
And partly this is because, despite undoubtedly being a sexually dominant woman, she also loves to please, and the orgasm is usually her method of delivering this pleasure- a pleasure she gives you, but to make herself happy.
Throughout her sexual life, she has been required to make men of all ages cum, and for a wide variety of reasons- to protect herself, to attract a man, to get rid of one; to make others jealous, to prove she is still desirable, to control a desperate man with an erection- but only when she is good and ready. Your orgasm, but her decision.
Loving cocks and manipulating a man via that base physical bond works for her at all kinds of levels. Usually jerking a man off would be seen perhaps as a submissive act, but this implies the owner of the cock has a say in how and where this happens; in Prims' case it will happen specifically when, where and how she demands, and she very seldom fails to induce a powerful and noisy emission when she has decided to empty your balls to her satisfaction. That's her satisfaction not yours- she may well go on milking you way after you think you have given her everything you have, just to see how you cope, just because she can.
Her fascination with cocks includes making them change shape and colour, for she will regularly slap, bite, kick, tie, tether, stretch and trample on them, just to examine your reaction. In this way one's cock and balls are often red raw and sore before she decides to finish the game by milking you- this trial, where the cock owner is unsure whether to scream in pain or pleasure, makes her very happy indeed. Her work is all about this conflict, and the battle of wills, using sex as the weapon.