Because that chain would be wiped out because if BIP-110 chain accumulates more proof-of-work, legacy chain would suffer deep reorg and see all its blocks orphaned. Its an one way street.
At first minority hash should make blocks generation slow which then drives the fees up, when mining on BIP-110 chain becomes more profitable, more hashrate migrates to BIP-110 chain which should raise the price and security of that chain.
So better for miners to switch sooner rather than later in order to avoid chain split.
Also if minority hash on BIP-110, fees on that chain are going to skyrocket due to slowly generating blocks so mining on it could actually become more profitable than mining on legacy chain. If hashrate migrates to BIP-110 chain due to higher profitability, price of that coin could continue to rise together with block rewards, creating positive feedback loop.
The fact that something is "within consensus" doesn't mean that it can't change Bitcoin fundamentals for the worse. FAFO-ing with mempool policy can also have terrible long-term consequences just like FAFO-ing with consensus can. That's why I think that this is perhaps the most important lesson we can learn from this war.
Gaslighting like "but it doesn't change consensus, what's all the fuss about?" simply doesn't hold water.