I guess this is the armchair psychologist thread then so here I go.
I think the main reason I have this fetish is because deep down I have a fear of making my own decisions and planning my life out. I remember a few years ago in a /d/ size thread someone asked if anyone would actually be into the idea of shrinking permanently in real life and a lot of people, myself included, said fuck no. Even though I jerk off to fantasies about that stuff the idea of completely giving up my life with no turning back is an obvious no-go.
But I've gotten older and I have to deal with a lot more responsibilities since then like working a full-time job and such, and now if I had to answer the same question my answer would be the complete opposite. If I had the option to give up my current life and just spend the rest of my existence being an inch tall worshipping the feet of some cute girl I'd take it in a heartbeat.