The post indicates WHATWG has "broad agreement" about removing XSLT. I don't know how many seats Google has there, but on the surface it doesn't sound like a unilateral decision.

Mozilla and others fell out of love with XML a long time ago. Deprecation of these technologies was probably inevitable after the WHATWG pivot and when they stopped adopting new XML tech. XML and related technologies got frozen in time and JavaScript took over.

The XML proponents lost this fight a long time ago. Without continued development, the user base shriveled up. Now that no one uses it, the runtimes are looking to cut dead weight.

I disagree with the pivot (RIP noscript) but it's not Google making this move unilaterally. It's been in the works for a long time.