Why is censoring of app reviews allowed?

Don't know. But I've seen lot's of poor reviews of apps, so I highly doubt that any outright censorship of poor reviews is ongoing.

It's possible that reviews are mdoerated (eg, for profanity), which causes a delay in the publishing of the review. And I'm don't think reviews stay published if the version of the app cahnges (you have to specifically select an "all versions" view to see old reviews).

And finally, there is a difference between ratings and reviews. The summary graphs show ratings, but not everyone who rates an app leaves a review. It's quite common for there to be far more ratings than reviews, by an order of magnitude, in some cases.

I am occasionally forced to give an app a 1 star rating. These reviews usually never show up. I am polite, courteous, and described the issues in detail. Moreover, I engage in no name-calling, or profanity. My 1 star reviews are rarely posted.

I do see one star reviews get posted. However, it appears that once a certain number of them are given for an application additional ones get blocked.

To answer your specific question as to why censorship is allowed. Remember, this is Apple's website and their hard drives, they have a right to control everything that goes on to it.