It's certainly fair to turn that question around, and ask what makes you think that it isn't? What else would you call a place where EVERYONE is a sinner, despite being repeatedly warned for thousands of years that all unrepentant sinners will join Lucifer/Satan/Iblis in The Fire?
We live in a world that we claim is a "civilized society" where people lie, cheat and steal from each other, where women are raped, children are molested, injustice is not only tolerated but promoted in every courtroom, and where the leaders of corporate fictions like church and state* are nothing more than professional liars and con-men. We've literally "legalized" theft in the form of taxes, licenses and fees, etc. and mass-murder in the form of war, which itself is a very lucrative business.
*church = all of the corporate fictional religions, their places of business (churches, synagogues, mosques, temples, etc.), and their sales staff (priests, pastors, rabbis, imams, etc.). And state = all of the corporate fictional governments of this world, at every level (city, state, federal and international).
Every single day we seem to descend to a new moral and ethical low, with true wisdom and common-sense becoming rarer and rarer. And the insanity is now growing at an exponential rate, with very few even bothering to ask why is all of this evil happening.
A "sinner" is just another word for a law-breaking criminal. And the world is a place from which none of us can escape.
Is it really not obvious that this is a prison reform school for the criminally insane?