It does seem like a pretty monumentally egregious invasion of privacy for them to leak taxpayer data for political reasons, but $14B seems crazy.
Also, you say it's an egregious privacy violation, but every other modern president released their tax returns willingly. Trump is bucking tradition here. As per usual.
The notion that it's a gentlemanly tradition means nothing. Codify it into law if releasing tax returns is such a big issue. In this case particular, I don't think the leaked tax returns have produced the effect that was desired, so it seems silly that this is what it has resolved to. I wonder if it ever mattered at all, given what we know about Trump nowadays.
Ultimately it's the rich people on the hill pulling all strings, the rest of us are just left to hold the bag.