The only reason the pref was there is that new features tend to have prefs to disable them. First because those are useful for enabling a feature for testing before it may be ready to be on by default, second in case there's a serious problem with the feature that requires it to be turned off in a hurry. But once a feature has been shipping and on by default for a while, prefs to disable it just end up being technical debt, and tend to get removed like any other technical debt when people get a chance.
This isn't even in my about:config anymore. I'm pretty sure it was at some point. Did they remove the option to disable it for some reason?