Hi. Non-writing fa/tg/uy here.
I don't speak for anyone else, but I'd note that, yeah, the LCB phenomenon got pretty popular. I don't know why anyone else liked it, but it appealed to me both on the surface--these two characters throwing away burdensome responsibilities they never wanted and fleeing the meatgrinder that is the battlefield, as a sort of antidote to the over-the-top, not-funny-any-more, overwritten, self-parodying GRIMDARK that is 40K.
And when we reflect on it further, these aren't particularly nice people, who don't particularly deserve to be happy. Taldeer in canon, in the game, is a horrible, horrible person, manipulative and cold-blooded, willing to sacrifice any number of lives for victory. And Vindicare assassins are basically noncommunicative autistic killing machines, man-shaped guidance and transport systems for a sniper rifle, willing to kill any number of innocents if ordered to do so. Both are basically monsters.
So, in the story, a chaos demon found it amusing to strip these things away from each of them and awaken each one's long-dormant, long-repressed humanity (eldarity?). Now all they have is each other, in an utterly uncaring galaxy, in which both governments want both of them dead just on general principles. They try to be happy anyway--and even have an a-d'awwwwwwwww-rable half-Eldar daughter and name her Lofn. Aww.