It seems likely to me that it is about the 'cost' - not literally monetary cost but one or two engineers periodically have to wrangle libxslt for Chrome and they think it's a pain in the ass and not widely used, and are now responding by saying "What if I didn't have to deal with this any more".

I'm not sure what else it would be about - I don't see why they would especially care about removing XSLT support if cost isn't a factor.