Because the Bitcoin Unlimited is a fork from the bitcoin itself. It's mean if that will disrupt the crypto community.
We do not need the Bitcoin Unlimited coin. It will be worthless in the future.
Well, if I were in charge of Unlimited I would start it off as a fresh alt and forget forking completely. Their blockchain could start in a similar way to Clams, take an image of every BTC balance and start from there.
That is exactly what a hard fork is about: take the balances of the previous coin, and apply a different protocol.