Why are you using the term "tame"?
She's straight and explicitly tells a female Shepard she has no interest in her. So naturally only a man can develop a romantic relationship with her. I don't think you need psychology lessons to know that people you have intimate relationships with are ones you naturally are more inclined to trust and feel comfortable around.
This is a stretch but it's fully possible that since Shepard herself is a woman, perhaps Jack did not want to feel patronized by her. I know my sister dislikes talking about emotional things with her female friends, but has that one (straight) guy friend who she feels comfortable around to talk to (and no they aren't involved). In any case, even an unromanced male Shepard does not break down her barrier so your point is moot.
I used "tame" in quotes because that what it looked like. She only experiences personal growth and closure if she has a romantic sexual experience with Shepard, and then she's nicer and more relaxed. Compare how she is with him to a female Shepard at the end of the game, and yeah, it looks like the game has written her as "tamed" by her new boyfriend. And my point was that a romance with a man "cures" or "tames" her, so no, the fact that she's bitter and closed off with an unromanced male Shepard, or one who only has sex without romance, doesn't take away from anything I'm saying.
It does happen in real life that some people only are able to feel close and open up with people they are romantically involved with...but if those same people are deeply troubled in the first place, pinning their emotional health on a new romance is a HORRIBLE idea. It's why people in recovery from addiction are told explicitly not to get involved in a new relationship for a while when they want to make a major change. It seems great at first, but after the first blush of new love fades, or the relationship ends, they are the same person as before, and the bottom falls out. Using a romance as a crutch as opposed to growing emotionally with or without Shepard isn't something to celebrate.
We're definitely not going to agree about this, which is why I generally don't talk about Jack with ME fans. I don't like how she's written, and I thought the message conveyed by her romance with Shepard versus how she ends her time getting to know an unromanced Shepard is pretty awful. That's all I have to say about that.