Two composer packages replace package X with * - why won't Composer allow this?

Question

In my main composer.json I include 2 packages that both replace package X in the following way:

"replace": {
   "package/x": "*"
}

Composer then errors with:

Only one of these can be installed: package/x[1.1.3], package/random-package-a[1.0.0], package/random-package-b[1.0.0]

I understand why this would conflict if the replacement was different in each package, but as it's the same (* in both), why won't Composer allow this?