I’ve already answered that one on Reddit 
I’m not dominant IRL. I’m a shy, introverted guy, always have, always been (to an extreme as a child, which lead to bullying and other unfun things). But seriously, that’s like… 90% of the reason why I enjoy the fantasy of shrinking women down - in my mind, when they are vulnerable, I can become confident with them, someone in charge, in control, and/or protective and assertive.
If you knew me IRL, you could never guess that I hide a dominant side.
I’m pretty sure the idea of shrinking someone, making them smaller, vulnerable, was born as a cope for my IRL social anxiety, introversion and extreme shyness. Imagining a place where I’m in control, confident, where I’m in charge, and having someone to care for and protect, is all that I’m lacking IRL. A shrunken woman can be my toy, a comfort plushie, a friend, a lover… And it’s always been a source of comfort to me, and the secret place my mind goes to unwind.