Why??

The author is making a point that they are the only ones who *aren't* insane. In the world of the story, they are the only ones who know the truth. Everyone else is forcing themselves to do things according to what will make them likeable, acceptable, and less lonely - like the MC at the beginning of the story. But it only makes them miserable and empty, or worse yet, liars who hide their true intentions to keep up appearances but are actually jealous and malicious. The point the author is making is that the main couple finally accept themselves as they truly are.

Thanks for this take, it pushed me to read it and i agree with you. Also I guess their world has supernatural phenomenon but as the world progressed it is forgotten and now our MCs encountered it and made use of them for their own happiness. It may really question your moral or ethics while reading this but thats the whole point, not evryone is good and willing to sacrifice their happiness for others, that i guess is why there are takers of happiness.