The U.S. Supreme Court determined that airports could not be considered a public forum to practice free speech. According to the ruling, airports exist solely for air travel and not for free expression.
Prior to the court’s decision, the International Society for Krishna Consciousness, a not-for-profit religious corporation, would often practice going into public places to distribute literature and asking for donations to support their religion.
Since 1992, airports across the country have adopted regulations governing speech, such as Lambert’s “Free Speech” booths.
To give them a designated spot to stay in so they're not wandering around bothering people waiting to collect their bags from baggage claim. It limits disruptive and frankly antisocial behavior.