Why? We don't need Bitcoin to be quantum proof for now because there's no actual quantum computer in our age. Google claiming that they have quantum supremacy doesn't mean anything to Bitcoin.
That's right as of now.
But think ahead. Quantum computing would possibly be the next thing. Prevention is better than cure as they say, and while it may seem quantum computing is still not a thing, researchers of cryptography should start thinking of methodologies and algorithms that would be considered quantum-proof. Because if not, then once quantum computer get a hold of the required computational power, time is shorter to protect the network.