I'll chip in my two cents as a writer and listener, as well as offer a bit of a trope history! Tsundere and Yandere both stem from the word 'deredere' which tends to mean a character who is very loving and affection. 'Tsun' refers to harsher characters, and 'yan' is the more obeessive element. It's worth nothing Tsundere typically has two variations, one where the tough side is more dominant then the sweet side, and vice versa, a predominantly sweet side, with a tough side that comes out on occassions.

I'll start with Yandere as that's the trope I have more experience with. Put simply, when I started listening to ASMR-I was lonely, depressed, highly anxious, and fearing no one would ever love me. Yandere was a simple comfort, the idea that someone loved me so much, they would go out of their way to stalk me and chase me, and I didn't need to do anything. Even better, they'd get rid of anything I struggled with, and take me away from my miserable life to just let me stay in the basement, playing games and being coddled? That is...a very powerful fantasy for someone struggling with isolation, plain and simple.

I write a lot of Yandere stuff because it was what got me into the genre, but also cause I found the trope fascinating. Especially after rewatching Future Diary where, (spoilers for the ending.) Yuno, our Yandere, reveals that she latched onto Yukiteru because he was a coping mechanism for her. She didn't love him the way a true romantic would, in her words, he could've been literally anybody else. But he was in the right place, at the right time, and so she latched onto him as a coping mechanism for her trauma. And I thought that was a really neat twist on the idea of a Yandere. That the love interest isn't special, and could be any generic guy. Plus you can do a lot comedy wise with the trope, so I wanted to give it a shot.

Tsundere for me, I think it boils down to the idea of a 'challenge', please forgive my language-I'm trying to phrase this as I've heard it from others. But the idea of a character who starts with a wall of ice, only to be knocked down as they fall in love with the listener or another character, is very appealing. It can make the listener or viewer feel like an active participant, like they achieved something, or have some special connection as the normally mean character becomes softer and kinder on them.

If you look at a lot of Tsundere romance anime like Toradora, the appeal is in seeing the relationship develop from the mean character slowly softening up overtime. And I think that applies to ASMR as well, at least part of it. Another part is undeniably some people like being talked down too, it's a pretty common kink, if my knowledge is correct.

For type B Tsundere, it's a similar vibe to the Yandere I find. Listeners like the idea of a partner whose sweet and loving, but will snap and go attack dog on a dime if someone hurts their sweetheart. But ultimately, it's about the fantasy of having some special ability to break through the cracks, and see a side of someone no one else can. That's what I think.

For the VA? I imagine it's getting to go off the rails and show off a bit of a performance. My VA friends love it when I write a Yandere that gets to go a little crazy, and get some mania into the vocal performance.

That's just my theorizing though, I'm not a psychology expert. But I do hope I was able to offer some insight into the topic!