Why doesn't WWX feel resentful the way he was treated if it were me I'd probably nuke the Jiang family bloodline
You know, this is something I actually appreciate very much about WWX as a character. Despite cultivating with resentful energy, he does not generally hold onto resentment himself. It's one of those neat ways he subverts expectations.
I do think this is a personality trait, but I also think that a lot of it stems from the statement of his mom's philosophy that he tells us in Chapter 113:
"My mom said you have to remember the things others do for you, not the things you do for others. Only when people don't hold so much in their hearts would they finally feel free."
Only when people don't hold so much in their hearts would they finally feel free. Resentment is a weight, you know? Holding onto pain and hatred and grudges can be a real burden. WWX doesn't want to hold onto that pain. He wants to move forward and build a new life.
He touches on this in the Second Siege of the Burial Mounds, in Chapter 82.
(Screenshot this time, because I don't want to type all that out. XD)
Either you hold onto hatred or you move on. What else can you do? With the Jiangs, WWX wants to move on. He doesn't have to forgive them (though I imagine he does, at least for what they did to him as a kid), any more than Fang Mengchen had to forgive WWX, but as long as he holds onto resentment, he is not free.
One of MDZS's major themes is about ending abusive cycles of hatred and violence, because all they do is cause more pain and hatred. The Wens attack the other sects, who first fight back and then up the ante by retaliating against civilians. Jin Zixun's grudge against WWX starts a chain of events that ends in the bloodbath of Nightless City and the First Siege of the Burial Mounds. Resentment and hatred and grudges have this way of building on themselves and getting bigger.
JGY's resentment for the way his family treats him turns into violence, including attempting to kill a shitload of cultivators in the Second Siege of the Burial Mounds just because they might find out about his earlier murders. Su She's resentment and envy of the Lans in general and LWJ in particular lead him to become an accomplice.
Jin Ling is one of the story's biggest symbols of the benefits of letting go of resentment. He starts off hating WWX for the deaths of his parents, and his personality reflects the anger and violence he's been steeped in, down to his complete lack of true friends other than his dog. But over the course of the story, he meets WWX and learns the truth and starts to let go of his hatred. We last see Jin Ling a more thoughtful person, with friends, building a good relationship with WWX, and a happier, better person all around.
Based on his narration, I don't know how consciously WWX recognizes how terribly the Jiangs treated him. If he doesn't, I suspect it is specifically because he wants to hold onto the good things they did for him, not the bad, because if he dwells on the bad he will not feel free.
As he tells JC about the core in Chapter 103:
Wei WuXian, "Uh, I think it's best if you...also stop keeping it on your mind. I know you'll definitely always keep it on your mind, but, how should I say it..." He clenched Lan WangJi's hand, saying to Jiang Cheng, "Right now, I do really think...it's all in the past. It's been too long. There's no need to struggle with it any longer."
For WWX, I think this applies to the Jiangs' treatment of him as well. It's all in the past, it's been too long, and there's no need to struggle with it any longer. He's got his future holding his hand and he wants to move on. He wants to be free.