There are things like Ring Signatures that already existed, other things came up later but had certainly never been implemented. At the time, there was also a conversation in Bitcoin about why all this wasn't being implemented, and the answer is the same as I explained above: if we implement this, then we can no longer guarantee that there will be a maximum of 21 million Bitcoins. The problem with hidden inflation is that it can occur without you realizing it, no matter how many cryptographic proofs you have in place to prevent it. It is a risk, hence the privacy-verifiability duality.