There have been some long posts about it. One over on Tackletour.com has an ongoing poll with results from what hands people use for each type of equipment.
I believe the common sentiment expressed is that some popular early spincast reels were almost always right handed reels, like Zebco reels many of us began on, then some of the older more expensive models, too, from way back.
I am a lefty, and many of us are a bit ambidextrous and I feel so happy that I cast both rods, spinning and bait caster rods, with my left dominant hand/arm, then reel with my off hand. I'm like you: I don't get the swapping of hands.