That data came to Meta through its Pixel code, which the tax firms installed on their websites to gather information on how to improve their own marketing campaigns. In exchange, Meta was able to access the data to write targeted algorithms for its own users.

https://apnews.com/article/irs-taxpayer-tax-preparation-meta...

Looks like very much more than "just negligence". Looks like deliberate private data usage without the consent of the people involved.