Very good read.. I too have seen this female behavior. Frustrating, But I have learned to catch it at an early stage and nip that shit in the butt.Sorry to disappoint you but you will get not hate from me for this issue. I'm also sorry to disappoint you that it seems that you're after a female perspective and sadly that is not one that I can give.
What I can tell you is that I sympathise with your situation. I've been in your very situation many-a-time before, though not so much nowadays. However, it's a very complicated, multi-faceted problem with, if I'm to be frank, no right answer.
There are a multitude of issues to consider.
The first is the obvious and direct question you raised yourself, why are there women that "let" themselves get physically, mentally or emotionally abused by men. I've put the "let" in quotes for a reason. More on that later. However, as for the question itself, I've learned from experience that it's a trap question for men, in a similar vein to "Does this make me look fat?". There is no right answer and even if you did have the right answer, the only acceptable answer is a canned response. In this case it's, "I'm not a woman, so I can't say".
The thing I find more interesting is not why women "let" themselves get abused but the corollary to that question - why are men abusing women in this fashion? Why are you frustrated at the women for being abused and not the abuser for not only doing the act but giving our gender a bad name? Why is it the woman's fault? One could consider that point of view as victim blaming.
Bear in mind there are two sides to this issue, so why isn't the other side being addressed? Have you offered to speak to these men to find out why they were so abusive for example? It's a rhetorical question but I hope you can see where this is going.
Then there's the age old dilemma of the "nice guy" syndrome. I take it that you are a reasonably young fellow? In my youth I'd thought much the same as you - I have female friends, they get along with me and I am kind and considerate and always there to comfort them and then they say those piercing words - why can't men be more like you? However, over time I've since learned what the nice guy syndrome is about at its core - it's part ignorance and part entitlement.
I'm being nice and considerate and caring. I spend the time to listen to women's problems. I console them and empathise with them. Why do they always go for the men that hurt and abuse them? They all say that they want to meet a guy like me. Why don't they like ME? Why won't they go out with ME? Why do the jerks get all the women and why is it ME that's left without anyone?
Here is perhaps a difficult question you should perhaps ask yourself sometime - are you being nice and considerate solely because that's how you are and that's what the situation calls for or perhaps because you think that this is your way into a potential relationship? Are they coming to you, not because they find this quality in you as attractive (but not enough to explore a more personal relationship) but because you have utility as a crutch to make themselves feel better.
Allow me to relay a story to you. Tell me if this sounds familiar.
There was a women I was friends during my high school years. We were never more than friends, mutually so, but we were otherwise close. She went out with another close friend of mine for a while but she broke up with him in a really bad way when she moved to another state. We would catch up when she would come to town. She would talk about this relationship she's having with some new guy she met. It would be an on-again, off-again situation. He was really disrespectful to her but she kept going for him. You know the story.
I would do what we men think is the reasonable and nice thing to do, which is to console and offer advice on how to deal with the situation or move on. Each time she would listen, nod and agree. Every time she would come back into town, the same thing would occur. More stories of the same person being on-again, off-again. more consolation, more advice etc. Every time we met.
I thought about it for a while and then it dawned on me. She actually didn't care at all for anything advice that I had to give her. I had mistaken my role as advisor. My role was to be a crutch; to feed her ego and specific need to draw sympathy and compassion from me for all the troubles she had with this person.
This went of for a bit until I told her one time point blank in a calm but frank manner "I'm wasting my time giving you advice because you're not going to take any of it? I'm supposed to just listen and say things like "that's too bad" or "I'm so sorry to hear it". "I'm your crutch, aren't I?". She thought for a moment and nodded sheepishly. It was then I'd realised through all our conversations, it was all about her and what was going on with her and not that much with me. While that day went on pretty normally after that, I've not heard from her since then. I'm not at all sorry that this was the case. A person that uses you in such a fashion is no person I'd ever want to associate with in any serious manner.
If this sounds very familiar to you, you may want to consider what your relationship is with these people. They may all be fine and perfectly good friends but it's something to consider none the less.
One last thing to ponder. Perhaps a question to ask these women. What is attractive and desirable of these men? Could it be their physical attractiveness? Physical strength or physique? Financial or social status? Assertiveness? They asked? Could the abusive situation be just a case of bad luck? If the situation is more chronic, why is that the case?
As I said in the beginning, no hate here. You do have my sympathies. I've walked that path before and asked those very same questions. Just be clear on what your role is with these women. Hopefully not as a crutch (well, unless you want to...). Try not to victim blame where possible. Also, maybe rethink the whole nice guy thing. There is a reason why they finish last.