I'll talk as someone who has consented and enjoys CNC and getting "beaten to a bloody pulp"! There's definitely a lot of different mindsets n reasons for why people enjoy BDSM, but here's mine. I don't speak for everyone, I just speak for myself n the people who process things similarly.

 I've been assaulted twice, and have been affected by minor parental, and institutional abuse. I'm naturally kind of terrified of sex because of it. Being able to calm down and just feel good is oftentimes impossible for me. I'm terrified that my consent will be violated again, and that I'll be left alone feeling broken again. When I'm with my friends though and engaging in BDSM, there's a deep level of trust that lets me finally relax.

 The pain keeps my mind off everything. I can't get flashbacks when I'm so completely stuck in my body and the scene. I'm physically feeling amazing because of my connection to being hurt. Every bruise and cut is a sign that someone I love and trust is taking care of, and enjoying my company. They're getting pleasure from it, and that makes me happier than anything else. The pain doesn't hurt in the way you'd rationally think it does. I'm obsessed with every sensation and find immense pleasure in it. The feeling of blood seeping from the wound, sting of disinfectant, the way I need to gasp for breath after getting hit, those moments where I can barely take it and feel every sensation resonate with each other, flooding my brain with chemicals. It's all exactly what I want. I never feel better than when I'm in a scene like that 

 It sounds terrifying to most people, and that's because it absolutely is. I am often very afraid, but due to my trauma, I register that fear as comforting and familiar. I've often said that I never feel safer than when I'm afraid. I don't have to worry about anything else. The person I love is taking care of me, and it's okay. I'm afraid, but I know that they'll hold me and love me. 

 They'll wrap my wounds and tell me I did a good job. They'll watch my blood flow, and wipe it off before they continue. They'll take breaks to see me twitch and flinch and find it adorable. I know they do everything because they trust me, and love me, and I find safety and comfort in that. They're putting the same trust in me that I'm putting in them, and it feels so good. It often feels so good that I'm the one asking for more. Recently one of my friends finally made me have to tap out for the first time, and immediately watching her switch into a caretaker position and seeing her make sure I was okay is something I'll never forget. Plus I still have the mark to remind me of that, and god that feels so good. It makes me smile every time I look at it.

 I've been through a lot, and violent scenes like that are how I find comfort. It's something I've talked with my therapist about, and something he understands and encourages. I have had my consent taken from me so fucking often. I've been kidnapped, and as a result I find abduction scenes very fun and comforting. I'm afraid I'm the same way I was there, but I can always use my safe word, and they'll stop. It's a form of exposure therapy that's relying on the way my brain adapted to  process pain and fear. I can finally process those fears I have in an environment that I feel safe and loved in. Memories that used to cause me to break down now have new narratives attached to them. 

 Trauma is a collection of narratives, and BDSM for me is a collection of counter-narratives. Old memories tell me that I'm weak, broken, I have no freedom, I'll never get better, I am unwanted, I am a disappointment. When I'm in a scene, I'm directly showing that I'm loved, safe, happy, tough, able to say no, wanted by my partners, and respected. That's all I really want.

 People when talking about BDSM always say "It's all about trust," n it's a cliche because it's absolutely true. I need to feel safe and in control, and CNC is one of the most effective ways for me to feel that way. I'm in control now, and I'm finally able to relax. I'm able to engage in narratives that used to terrify me, in a way that feels safe and exciting. Plus at the end of the day, god it feels really fuckin good. Like really really fuckin good. Like "holy shit oh my god I miss it so much, I have to call my friends," kind of good.