I don’t see any actual answers to the question asked. Though, admittedly, this makes sense since any answer would necessarily have to be speculation, and this is GQ.
That said, I will speculate. If they keep forcing a setting reset on you, that suggests that there is something detrimental to Facebook about that particular option. They don’t want to risk you switching the setting and then forgetting about it, staying in that mode.
So why might someone always using “Most Recent” be detrimental to Facebook’s bottom line? The first idea is that people who constantly see less interesting stories are less likely to stick around. Facebook has always valued people using their site as long as possible. My next idea is that it messes up advertising, which probably depends on figuring out what is most popular. The ad model depends on seeing how wide something goes, and, by choosing “most recent,” you’ve essentially opted out of seeing the ads with the highest reach.
So they want to make sure that anyone who is using “Most Recent” has to choose to use that mode, meaning they are consciously aware that there is other higher rated content out there. They will say active. And, the next time they log in, it will be reverted, so they’ll still see the highest stories for at least a little bit of time–so the ads in your feed have at least some time to work.
Obviously, Facebook isn’t hurting for making this decision, and thus has never had to balance the issue. Heck, having third party properties that change this setting is probably a blessing to them, as it keeps people who actually are dissatisfied from leaving, but means the average Facebook user will not get stuck in the non-preferred mode.