Why does the cycle keep going on? And what's the cause of it. Is it because of they were abused of their parents and so on?
There's a short answer and a long answer.
Short answer: Humans tend to follow patterns that they've learned throughout life, including destructive ones.
Long answer: It's really damn complicated. Humans are both predictable and unpredictable in what they'll do to themselves and others. Nothing excuses the behavior, and no matter how badly a person is treated, no one should be subjugated to that kind of treatment.
Sometimes the person who does the abusing, and was likely abused when they were younger, doesn't even believe that they are being abusive; their behavior is considered a norm. An example of this that I can think of is my mother and her family. My mother treated my sister and I like shit, like threatening to hit, saying that if we don't do X, then we'll get what's coming to us (I left a door unlocked one night by accident and she said that I'm lucky I didn't get raped. I was 16/17 at the time), and shouting about everything that was wrong with us. I remembered one time I was yelled at for three hours because I *gasp* dared to have a social life as a high school freshman. I then had to prove myself "worthy" to stay within her house, or I was off to my bio-dad's place (I was terrified of him at the time). Because of that, I stopped going out and talking to people, because I was afraid the truth would get out. It got to a point where I used to joke that it wasn't a full day until I got yelled at. Eventually, I had to go to counseling on campus because it began interfering with school work when I was a sophomore in college. I never understood why she did what she did until I watched and listened to all the dirty laundry her family had.
Her mother did the same thing to her and her siblings, as well as her father (who did numerous other things that I won't mention), and I firmly believe that it influenced a lot of things in her life. The biggest one that is apparent to all is her choice in men, mainly the last two. Any "good man" she's ever had, she's abandoned (my brother Dustin's father in particular). Unsurprisingly, her mother up to her great-great-grandmother were terrible judges of character when it came down to selecting a husband.
Fast forward to current day to see the damage. My oldest sister Michelle, who was raised by her great uncle and his wife (that marriage fell apart because...abuse...shocking), has had a life of hardships. She's happily married, but she is always wary of herself and how she treats her husband and kids. My brother, Dustin, who is also happily married with a daughter, keeps everyone at arms length (I think I've spoken to him about once or twice?). Amanda, my older sister and guardian angel in human form, deals with anxiety, depression, and a whole host of other issues while being married, taking care of three kids under the age of six, and going back to school to get a good job so that her family can finally get out of poverty. Then, there's me. I have spent most of my life trying to ignore what's happened by burying myself in academics and sheltering myself from the world. Sure, I can tell you a bunch of book shit, but I have to ask how basic romantic/platonic/hell, normal relationships work constantly, along with a bunch more fun lovely stuff. However, each of us does what we can to break that cycle and discover what "normal" is supposed to be.
Perhaps the reason it makes you angry so much is that you're trying to find rational answers to things that are irrational. It's doesn't take a rocket scientist to figure out that just because someone treated you like shit doesn't mean you have to continue that behavior. And yet, society continues to see the product of broken homes and people every generation. To make a long story short, there isn't a definitive answer. Because for every person that exists, there will be just as many reasons why things like this continue. The best you can do is be kind to those in need and to let go of whatever you're holding onto. It's not keeping them (those that hurt you) up at night, only you.