Thir, I don't have any experience of this but I found your question interesting and it made me wonder...

Could it have something to do with the extravagant claims you sometimes hear from both subs and doms about how they were born to their mindset, they've always knows they were definitely one or the other, they're sub or dom to their very heart and soul, it fulfils/completes them to their core, etc etc (which may be true but that's the orthodoxy it's so easy for any old sub or dom to tag themselves with) - so when there are those few who claim to be able to genuinely and meaningfully switch between the sacred engrained positions, it rather seems to undercut the deadly earnestness of these positions, and nobody likes to be 'cut down to size.'.

Am I on to something here, do you think?