Gecko is not just a web engine; it is in many ways an entire application framework. Gecko inverts control such that it implements the entire main event loop of the application. Desktop Firefox is essentially one big privileged HTML+JS application that happens to embed a non-privileged browser iframe within it. about:config governs settings around everything in this framework.
Now let's look at Android: the modern architecture of Firefox for Android is that of a native Android app that embeds Gecko similarly to a WebView, albeit a much more powerful one (GeckoView)[1]. Many parts of GeckoView's implementation need to deal with reconciling the "Gecko as app framework that controls the universe" paradigm with the "Gecko as a lowly Android View rendering into a graphics surface" paradigm. about:config is still important, but it only affects the Gecko part, not the native app part.
For GeckoView to work correctly, many about:config settings must be set to very specific values -- the free-for-all that is about:config on desktop could actually break an instance of Firefox on Android. This is particularly fatal to an app when run on a non-rooted phone.
Yes, people have come to accept shitty software. You'd think that software developed for the public good would try to be better though and at least retain the old standards for power user tools.
I don't think it's unfair to say that that's basically correct.
