I'm reminded of a cartoon in my counselling newsletter... A couple's eyes meeting across a crowded room... Both of them thinking "What a divinely damaged person!"
Some relationships are based on playing the "patient/healer" game. By its nature, D/s lends itself to these roles. That doesn't mean that a sub needs to be damaged, just that a sub who enjoys playing the "patient" will find plenty of Doms happy to play that game.
We all have our dents and creases in our personality, and we are naturally happiest in a relationship that fits them. That goes for Doms as much as for subs: I know just which of my old damage patterns are satisfied by dominance and which by submission. But that's separate from the reasons I am a switchy Dom.