Ethereum has been build for 'future' with resilience in mind. For address generation (i.e. public-private key pair), Elliptic Curve Cryptography (ECC) is used, and besides other reasons, its performance is far superior to other existing algorithms (for example, RSA-based).
Even though no flaw has been found in the Elliptic Curve algorithm used in Ethereum, the founding designers wanted to keep the system resilient in case a flaw/ exploit in the algorithm is detected so that no one can reverse engineer the private key from the public key. Because the hashing algorithm has already been proved to be immune to reverse engineering, adding this on top means that no one can go back to the private key from the address (even if the ECC algorithm were exploitable).