Bitcoin unlimited = Hardfork
Hardfork is quite risky if there is so much debate between community like we have right now.

Community is divided between two distinct solution BU and Segwit, so hard fork may quickly lead to loads of attack on both chains which doesn't give good impression among bitcoin holders who don't know much about technological side of bitcoin and about all this forks.

It is not a good time to split the bitcoin network, so BU is not a good solution.