In the Bitcoin whitepaper, Satoshi Nakamoto proposed using a one-time address-key pair for each transaction to enhance anonymity.
As an additional firewall, a new key pair should be used for each transaction to keep them from being linked to a common owner. Some linking is still unavoidable with multi-input transactions, which necessarily reveal that their inputs were owned by the same owner. The risk is that if the owner of a key is revealed, linking could reveal other transactions that belonged to the same owner.
Why isn't this implemented in Bitcoin Core wallet or enforced as a verification rule? The implementation can significantly enhance privacy, although not as anonymous as Monero but definitely will make chain analysis much harder and costly. And it won't compromise security.