it is the only sane thing to do. Allowing everyone to use their own fork means when a major bug is found you have to fix thousands of forks. If the bug is a security zero day you don't have time.
I don't see how being forced to upgrade all consumers is a good thing.
It forces implementers of broad or disruptive API or technical changes to be responsible for the full consequences of those decisions, rather than the consumers of those changes who likely don't have context. People make better choices when they have to deal with the consequences themselves.
It also forces the consequences to be incurred now as opposed to 6 months later when a consumer of the old library tries to upgrade, realizes they can't easily, but they need a capability only in the new version, and the guy who made the API change has left the company for a pay raise elsewhere.
As a plus, these properties enable gigantic changes and migrations with confidence knowing there aren't any code or infrastructure bits you missed, and you're not leaving timebombs for a different project's secret repo that wasn't included in the gigantic migration.
Bluntly, if you can't see why many people like it (even if you disagree), you probably haven't worked in an environment or technical context where mono vs poly truly matters.
Mapbe but each one now is another thing that you need to fix if a major issue is found. If it is only a few releases not a problem but it can get to hundreds and that becomes hard. Particularly if the fix can be cherry-picked cleanly to other branches.
Seems like a big restriction to me.