BU is just a code implementation,

there are MANY
core, knots, fibre, bitcoinj, bitcoin ruby, BTCd, nbitcoin, statoshi, bitcoinxt, bitcoin classic, bitcoinunlimited... and so on.

bitcoin unlimited has set no deadlines, set no schedule of activation. has no zealous banscore tricks, no intention to cause a split.
bitcoin unlimiited wants consensus of many diverse nodes all on one PEER network. (bitcoin remaining diverse open and decentralisation)

however core feel its a threat to their segwit plans of a TIER network of core being the upstream filters, in control of validation and changes in future direction. so core are on the rampage fearing their loss of control..
(there should be no control anyway so anyone arguing core deserve control doesnt understand bitcoin. and is obviously involves in centralising bitcoin)

core first intentionally avoid hard(node+pool) consensus(vote) and went only for soft(pool) vote
then core uses bip9 that has some intentional banning pool/block features to turn their majority to 100% by killing off the opposition.soft(pool) contraversial

core next realised that pools were still unofficially(but a good reasoned safeguard) waited to see what node counts suggested before deciding.
so now core are going heavy. UASF and even as far as PoW algo changes hard(node+pool) bilateral split. to threaten the pools to vote for core or be struck off the network.

and now core see BU as a threat, because its giving the community another option. and risking cores dictatorship.

funny parts to remember.
1. core gave pools the vote so dont blame pools for saying no to core
2. core failed at bribing the community with fee discounts. while cunningly pushing fee's up to counter the discount
3. core will be the ones triggering the splitting of the network rather than accepting a no answer,
4. core are ignoring community views of wanting something else. because it doesnt follow the core corporate roadmap of centralised LN services to repay their $70m+ debt

meanwhile BU will keep on plodding along with no intention to do anything unless there is majority consent