The only way for everyone to follow precisely the same rules is for every node to be share the same consensus implementation.
but if everyone was following the exact same code.. EVERYONE gets affected if there was a bug
EG the 2013 event happened because everyone was virtually core managed..
however imagine if there were some 0.8 (leveldb) nodes and btcd(wrote in GO and leveldb storage) the network would continue and make blocks and only the 0.7(which would have been less majority, if more diversity existed)) would have been left unsynced. and it would have been far far easier to just say "hey 0.7 time to upgrade"
by having diversity, only the non rule following nodes get kicked off the network or cant sync.
EG assert bug was not a network wide bug because of diversity
thus bitcoin continues due to diversity and only the problem code implementation would stop.
diverse decentralised peer network has its reasons to be diverse and decentralised.
the only advantage of everyone centralizing the exact same code line for line. is to make changes easily without veto because everyone would be forced to change without choice.. which also has its own risks and exploitability by doing this.