The only alternatives, besides Excelsior, is the new RoboVM, Websphere Realtime JVM, Aicas, Aonix among a few other ones.
And if Graal eventually replaces Hotspot on the reference JVM, it might be that Truffle comes along as well.
Heck, the runtimes you're advocating are generally installed as binaries. If they can get updated, then so can any other binary.
And if a user doesn't bother to update a given application's binary when a critical flaw of some sort is found, then there's a very good chance they wouldn't bother to update any runtimes that are installed, either. This is true even when some sort of update notification and installation process is offered. The end result is the same in either case: the update is not applied.
Runtimes shouldn't be portrayed as any better in this case, when they're generally no different than any other binary.