The other suggestions ignored seemed to be "if this is about security, then fund the OSS, project. Or swap to a newer safer library, or pull it into the JS sandbox and ensure support is maintained." Which were all mostly ignored.
And "if this is about adoption then listen to the constant community request to update the the newer XSLT 3.0 which has been out for years and world have much higher adoption due to tons of QoL improvements including handling JSON."
And the argument presented, which i don't know (but seems reasonable to me), is that XSLT supports the open web. Google tried to kill it a decade ago, the community pushed back and stopped it. So Google's plan was to refuse to do anything to support it, ignore community requests for simple improvements, try to make it wither then use that as justification for killing it at a later point.
Forcing this through when almost all feedback is against it seems to support that to me. Especially with XSLT suddenly/recebtly gaining a lot of popularity and it seems like they are trying to kill it before they have an open competitor in the web.