Because of the impact their actions have on people's lives.

If my local barber tells me "don't come back here ever again", I'll find another barber within 15min walk from my place.

If Facebook bans me, I might lose a way to communicate with hundreds of people, I might lose access to managing my business and talk to my clients. And often there might be very few viable alternatives.

As Facebook and other large companies become dominant in certain areas, their responsibility should grow, too. And banning users based on some algorithmic detection, without the ability to contact human customer support to understand and fix the situation, should not be acceptable.