Question: Do you know why Avery is so obsessed with MC?
There's a mysterious charm to the MC that attracts the gaze of others. It's why pretty much every LI except for Sydney, Robin and to an extent Alex is obsessed one way or another with the MC. Bailey knows of the mysterious charm the MC has as well, and so that's why they try to capitalise on the MC the most out of the others.
As for why Avery specifically is so obsessed with the MC, it's likely because of Bailey. Perhaps Bailey had shown pictures of the MC to Avery, just like how they did to Eden - I'm pretty sure Eden's obsession with the MC is because of that one time they came to visit Bailey, lonely from their isolation in the Forest, and was shown a bunch of photos of the orphans living at the Orphanage which included the MC's, and had been captivated since then.
For Avery, perhaps it was the same thing. Or perhaps it's more of Avery is aware that Bailey places a certain importance to the MC compared to the other orphans, and with Avery's greed for 'societal elite' power, see the MC as nothing more than a 'way in'. Having the MC as their trophy husbando/waifu would be having some leverage over Bailey - after all, when Avery takes the MC into their mansion, it forces Bailey to visit them every week to ask them to pay for the MC.