WGM is my absolute favorite KShow and I've seen all the episodes I could get my hands on so I have a lot of theories about this but I'm afraid of looking like a crazy person for analyzing it so much or if I name specific couples I'll bum people out... but I'll try and say this as concisely as possible without naming names...
I feel like there are a couple of different types of couples on the show, there's the probably gay guy who's doing the show to stop rumors and they have lots of fun. There are couples where it seems one partner simply resents the other and hates their manager for making them do the show and are trying to get it over with as quickly as possible. There are couples who are very stiff and shy probably out of fear of upsetting their fans or getting in trouble with management. There is one couple (two if I'm honest) that I would bet actual money they were fooling around when the cameras were off.
And then there's 2young who is the type where it's just apparent that they have real chemistry and genuinely enjoy being around each other. I would just imagine that living the weirdly secretive lives that idols lead would make getting to go on a public date every other week an amazing experience. They would be crazy not to really make the most out of the experience, and it makes perfect sense that the well matched couples might develop real feelings for their virtual spouse
I don't know if any of that made any sense, all that has just been sitting in my brain forever and i've never had to articulate it before. UGH also so long. sorry about that.