The better question is, why should Lobov be anywhere BUT the the prelims?
Lobov should be extremely thankful he's even still in the UFC, because he certainly shouldn't be. Look at the names who the UFC has let go or allowed to walk away... if you're letting a guy like Mousasi leave and keeping Lobov, there's a severe fucking (mis)management issue. I'm glad Mousasi left for better money and terms, but it sucks that it came to that.
The Endeavor-led UFC wants a few big draws and a bunch of fighters wililng to fight cheap, whether they are no-names or fighters taking less than they deserve. Look at all the recent cards and events, the well-known fighters seem to be disappearing or not scheduled, and the UFC is using second and third tier locals to fill up a card because they come cheap and stupid... just the way the UFC likes them. The UFC keeping Lobov is obviously a blatant move to placate Conor and for no other reason.