That's a deep rabbit hole that leads to the Underdark (https://en.wikipedia.org/wiki/Underdark) of Enterprise Legal Agreements.
Only high-level legal wizards and magisters can go there and expect to understand anything and keep their sanity.
Not a lawyer, but I expect it comes down to "if you follow our guidelines and pay us enough we can make the following guarantees, but there are certain things that we simply do not cover."
This is exactly what a warranty is though.
Yes, but it is not for consumers. It is for big businesses that pay millions and have specific expectations. The more you are willing to pay to more you can get within specific limits.
Your original statement, "If you pay for software it generally comes with some warranty and guarantee of fitness for purpose." does not hold for consumers and only partially holds for enterprise customers.
It might be better stated: "If your business / entity / government has specific needs (e.g. compliance with legal or medical regulations, industry certifications, ISO requirements, auditing, etc.), has a large sack of money to pay, and a team of lawyers, then there are some software publishers who will sign contracts to guarantee you certain qualities about the software you license with them and perhaps some level of support of that software."