Just to give some more details, this is a one-time thing to rectify the situation that a lot of old versions of packages had no compat bounds at all. So what could (and quite frequently did) happen was that the resolver (the algorithm in the package manager that figures out what versions to install) found a really old version that had no compat bounds, got happy because that version claimed to work perfectly in the current project (because of no compat bounds), and the resolver then installs that many-year-old version and people get confused why things are not working.
Now, those old versions have compat bounds and should no longer be picked by the resolver.