They don't need to.
Because they already have on several occasions, even though it means that their conversation happened in bits and pieces. When Asad came to find Zoya at SM for the first time, she yelled at him about how wronged she felt, and how he shouldn't have let anything come between them like that. And he listened, and he accepted his mistake, and he apologized for it.
Then later when they met at the hospital after Ayaan collapsed, we heard a new development in the story: Zoya's confusion. Which she shared with Asad clearly, and he tried to assure her that it would be alright, even though it wasn't clear then whether he was sure himself.
So Asad had allowed other things to come between the two of them, and Zoya was confused between her idea that marriage is forever and her love for Asad. What now?
Asad's realization happened when Najma spoke to him, and he realized exactly how completely stupid he was for letting anything come between them, even muqaddar. So he marched up to SM and expressed this very thing very clearly to everyone there, including Zoya. After Zoya returned to SM, he reiterated that he would never let circumstances come between them again.
Zoya's realization happened the moment she realized Asad had stopped thinking about the whole world and finally made her a priority. When he did that, that's when she realized that she'd choose Asad over her idea of marriage any day. Which she expressed clearly to everyone there as well, including Asad.
Maybe it seems like Zoya forgave Asad too easily, and that she should've made him grovel for her forgiveness. But there are two things that stop this from happening. One, Zoya had made mistakes too, she wasn't completely innocent in the series of events. Two, Zoya herself wouldn't want Asad to grovel. You know why? Because it would just hurt her more to see the person she loves in that state. Think about it, if you've been wronged by a loved one, compared to being wrong by a stranger/acquaintance, wouldn't your reaction be different?
But maybe there are some things left unsaid. Like Zoya's acceptance of her own mistakes. Or Asad's private apology to Zoya. But they still won't discuss it anymore. You know why?
They don't want to.
Just in the last episode, Ayaan explained how thinking too much is sometimes bad for you. The same applies here. Zoya is finally back in KV, and they don't wanna harp on the past anymore because all it gives them is pain. Bringing it up would just be like scraping at wounds that are badly trying to heal. So they've just decided to let it go.
Sometimes when my sister and I fight, we end up saying unspeakable things to each other. Yet we patch up eventually, not by talking about the fight, but by ignoring the fact that it even happened. It might sound immature, but sometimes the easier thing to do with loved ones really is to just let it go. I mean, how much longer can you go on without them?
Besides, not letting things go can be really unhealthy. Asad's held a grudge against his father all these years, and all that this grudge has given him is misery. Shirin's held a grudge against Dilshaad and now even Asad for many years too, and look at how miserable that has made her! It's all she can think of and it eats her up inside.
The best part is, Asad and Shirin are holding grudges against people they don't even like to begin with. Can you imagine how much more emotionally draining it would be to hold a grudge against your own loved one? Dilshaad held a grudge against Asad for a whole month after Asad and Zoya's first failed nikaah. She was already upset about Zoya's absence, and the fact that her own grudge stopped her from consoling Asad made her even more miserable.
All I'm saying now is that I don't see a need to hold a grudge against Asad and Zoya for not talking it out, when they themselves aren't holding a grudge against each other. Isn't a good thing? Besides, once a grudge is dissolved, what follows is happiness. Asad and Zoya are happy now, after a very long time. Happiness can be pretty infectious, if you'd just give it a try (:
But then maybe they should at least talk about that and clear the air. But they still won't. You know why?
The makers don't want to.
They took an extremely bold step when they decided to go ahead with Zoyaan. The TRPs stayed the same and even rose at a point when that happened. But after a while, they started to fall, and they realized they had to wrap up the track.
Sure it's easy to say that if they'd taken the step they should've stuck to their guts and followed through, and not give in to pressure of ratings. But this is easier said than done. Even if they wanted to, the channel would tell them otherwise.
This show is merely a form of entertainment for us, but for them, it's their bread and butter. Sometimes they have to give in to the pressures of the industry in order to survive. After moving Zoya back to KV, if they still chose to harp on the failed Zoyaan track, it would defeat the purpose of bringing Zoya back to KV to begin with. So they're choosing to ignore it.
It is the sad truth, Indian television serials run based on TRPs, and their success is measured by how long they stay on air. So I don't blame them this time, and I'm not gonna hold a grudge against them for not making Asad and Zoya talk it out. Maybe it'll still happen in the future, maybe it won't. But I'm not gonna harp on it, because it's the easier thing to do (: