Alright, alright. Let me preface this by saying I am starting this discussion because I am purely curious and just want to discuss this with anyone else who has thoughts on the topic. Please, no negative or mean comments. Let’s respect the opinions of others. We watch BLs, so we must be an open-minded, sophisticated group of mutuals… right? 
Another preface is that I am an avid BL watcher who has been on the Thai BL train since the days of Sotus, Love Sick, and Together With Me; however, I have no in-depth or expert knowledge of the Thai BL industry. If you do, please, by all means, shower me (us) with knowledge. 
Ok, so! If you know Thai BLs, you know that they took the concept of an OTP and really said yes. 
K-dramas are also doing this, but not to the same degree, I don’t think. I’m talking about pairings like Joong and Dunk, Tutor and Yim, New and Tay, etc. These are just some off the top of my head. Bear in mind I am not targeting these actors, nor am I saying their performance/casting is wrong/bad/undeserved. Not at all! I don’t have that kind of negativity in my BL-loving heart, ok? This is about the trend of Thai BLs to recast the same two male leads.
My question for this has been, are they casting two actors that fit the role of the drama, or are they choosing the actors primarily based on their popularity as a pairing among fans? And what about the other talented actors who are missing out on a chance to shine because the same group of leads are casted? These are just things I have imagined as potential issues with recasting the same couple again and again. Are they real problems? I don’t know.
Another thing that I have noticed is, after seeing the same couple in many shows, when they do branch out and pair with a different actor, it’s like wait, why aren’t they with X? It almost feels like their character becomes attached to the other, just like how fans put the names of these OTPs together, i.e., JoongDunk. Do you guys feel this way too?
Well, these shows need to be popular and make money, you might be thinking. And yes, I can see how that is the case. Also, I loosely know that these Thai acting/production companies will have a pool of actors and actresses (a sort of household) that they will pick from when creating a new show, so that might be part of this (How accurate is this? Anyone know?).
Still, we can’t not mention the undeniably perfect and what some would call one of the OG Thai BL pairings, Max and Tul. Same goes for Off and Gun. The chemistry and originality in the roles they play are hard to deny, but I suppose, despite my bias toward them, the same discussion could be had. But I mean, I don’t know of a series where Tul and Max didn’t fit their roles perfectly… just saying, lol. I guess my grievance is with recasting that feels too forced, though how to measure that would also be subjective.
As you can see, there’s no real argument that I am trying to make, lol. I’m not sure if I am against or neutral to this topic. It’s case-by-case.
What are some other OTPs that you have seen in Thai BLs, and what are your thoughts on this? Do you think there are pros/cons to recasting the same male leads? Why do you think this is a trend in Thai BLs?