See Brendan's response to me last week[0], which I think comes down to feature set they want to support rather than do all the work it would require to build that in servo now (they went from gecko [no public info on this] -> electron -> and now chromium. they would have to migrate from chromium -> servo).
I wish they did, and just cared less about all the other features that were missing from gecko (but that's just be being selfish and not wanting to build out native stuff myself lol)