The point is that all this is not seen as valuable by users and market leaders. You don't gain marketshare in b2c by saying "my gizmo is more memory-safe than other gizmos", you have to show features. Chrome's process-separation was a feature: you could easily dispose of non-responsive pages, which other browsers couldn't do as well. Even then, it wasn't really why Chrome took off - it took off because of deep integration with Google's ecosystem, incessant marketing efforts, and monopolistic behaviour (Google "unwittingly" breaking GMail and other G products on other browsers, on a regular basis).
So what feature would full memory-safety actually enable? I suspect that's the bit that the Servo folks couldn't articulate well enough.
